diff --git a/NAMESPACE b/NAMESPACE
index 2b77d638c8..32975e811c 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -476,7 +476,6 @@ export(is.facet)
 export(is.ggplot)
 export(is.ggproto)
 export(is.theme)
-export(is.waiver)
 export(is_coord)
 export(is_facet)
 export(is_geom)
@@ -492,6 +491,7 @@ export(is_scale)
 export(is_stat)
 export(is_theme)
 export(is_theme_element)
+export(is_waiver)
 export(label_both)
 export(label_bquote)
 export(label_context)
diff --git a/NEWS.md b/NEWS.md
index 4d630967a8..e75e082bcd 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -92,7 +92,7 @@
   @yutannihilation's prior work, #3120)
 * When discrete breaks have names, they'll be used as labels by default
   (@teunbrand, #6147).
-* The helper function `is.waiver()` is now exported to help extensions to work
+* The helper function `is_waiver()` is now exported to help extensions to work
   with `waiver()` objects (@arcresu, #6173).
 * Date(time) scales now throw appropriate errors when `date_breaks`,
   `date_minor_breaks` or `date_labels` are not strings (@RodDalBen, #5880)
diff --git a/R/aes.R b/R/aes.R
index de3376071d..33eae1de83 100644
--- a/R/aes.R
+++ b/R/aes.R
@@ -302,7 +302,7 @@ aes_ <- function(x, y, ...) {
   caller_env <- parent.frame()
 
   as_quosure_aes <- function(x) {
-    if (is.formula(x) && length(x) == 2) {
+    if (is_formula(x) && length(x) == 2) {
       as_quosure(x)
     } else if (is.null(x) || is.call(x) || is.name(x) || is.atomic(x)) {
       new_aesthetic(x, caller_env)
diff --git a/R/axis-secondary.R b/R/axis-secondary.R
index c1d024e288..d694cf3a47 100644
--- a/R/axis-secondary.R
+++ b/R/axis-secondary.R
@@ -124,19 +124,19 @@ dup_axis <- function(transform = identity, name = derive(), breaks = derive(),
   sec_axis(transform, trans = trans, name, breaks, labels, guide)
 }
 
-is.sec_axis <- function(x) {
+is_sec_axis <- function(x) {
   inherits(x, "AxisSecondary")
 }
 
 set_sec_axis <- function(sec.axis, scale) {
-  if (!is.waiver(sec.axis)) {
+  if (!is_waiver(sec.axis)) {
     if (scale$is_discrete()) {
       if (!identical(.subset2(sec.axis, "trans"), identity)) {
         cli::cli_abort("Discrete secondary axes must have the {.fn identity} transformation.")
       }
     }
-    if (is.formula(sec.axis)) sec.axis <- sec_axis(sec.axis)
-    if (!is.sec_axis(sec.axis)) {
+    if (is_formula(sec.axis)) sec.axis <- sec_axis(sec.axis)
+    if (!is_sec_axis(sec.axis)) {
       cli::cli_abort("Secondary axes must be specified using {.fn sec_axis}.")
     }
     scale$secondary.axis <- sec.axis
@@ -150,7 +150,7 @@ set_sec_axis <- function(sec.axis, scale) {
 derive <- function() {
   structure(list(), class = "derived")
 }
-is.derived <- function(x) {
+is_derived <- function(x) {
   inherits(x, "derived")
 }
 #' @rdname ggplot2-ggproto
@@ -182,9 +182,9 @@ AxisSecondary <- ggproto("AxisSecondary", NULL,
     if (!is.function(transform)) {
       cli::cli_abort("Transformation for secondary axes must be a function.")
     }
-    if (is.derived(self$name) && !is.waiver(scale$name)) self$name <- scale$name
-    if (is.derived(self$breaks)) self$breaks <- scale$breaks
-    if (is.waiver(self$breaks)) {
+    if (is_derived(self$name) && !is_waiver(scale$name)) self$name <- scale$name
+    if (is_derived(self$breaks)) self$breaks <- scale$breaks
+    if (is_waiver(self$breaks)) {
       if (scale$is_discrete()) {
         self$breaks <- setNames(nm = scale$get_breaks())
       } else {
@@ -197,8 +197,8 @@ AxisSecondary <- ggproto("AxisSecondary", NULL,
         }
       }
     }
-    if (is.derived(self$labels)) self$labels <- scale$labels
-    if (is.derived(self$guide)) self$guide <- scale$guide
+    if (is_derived(self$labels)) self$labels <- scale$labels
+    if (is_derived(self$guide)) self$guide <- scale$guide
   },
 
   transform_range = function(self, range) {
diff --git a/R/coord-radial.R b/R/coord-radial.R
index cecef3d9b2..e1ccd1eb67 100644
--- a/R/coord-radial.R
+++ b/R/coord-radial.R
@@ -576,7 +576,7 @@ deg2rad <- function(deg) deg * pi / 180
 # Function to rotate a radius axis through viewport
 rotate_r_axis <- function(axis, angle, bbox, position = "left") {
 
-  if (inherits(axis, "zeroGrob")) {
+  if (is_zero(axis)) {
     return(axis)
   }
 
diff --git a/R/coord-sf.R b/R/coord-sf.R
index 12019a64d8..16967cda8c 100644
--- a/R/coord-sf.R
+++ b/R/coord-sf.R
@@ -116,7 +116,7 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
     x_breaks <- graticule$degree[graticule$type == "E"]
     if (is.null(scale_x$labels)) {
       x_labels <- rep(NA, length(x_breaks))
-    } else if (is.waiver(scale_x$labels)) {
+    } else if (is_waiver(scale_x$labels)) {
       x_labels <- graticule$degree_label[graticule$type == "E"]
       needs_autoparsing[graticule$type == "E"] <- TRUE
     } else {
@@ -141,7 +141,7 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
     y_breaks <- graticule$degree[graticule$type == "N"]
     if (is.null(scale_y$labels)) {
       y_labels <- rep(NA, length(y_breaks))
-    } else if (is.waiver(scale_y$labels)) {
+    } else if (is_waiver(scale_y$labels)) {
       y_labels <- graticule$degree_label[graticule$type == "N"]
       needs_autoparsing[graticule$type == "N"] <- TRUE
     } else {
@@ -335,7 +335,7 @@ CoordSf <- ggproto("CoordSf", CoordCartesian,
 
     # we don't draw the graticules if the major panel grid is
     # turned off
-    if (inherits(el, "element_blank")) {
+    if (is_theme_element(el, "blank")) {
       grobs <- list(element_render(theme, "panel.background"))
     } else {
       line_gp <- gg_par(
@@ -554,7 +554,7 @@ coord_sf <- function(xlim = NULL, ylim = NULL, expand = TRUE,
                      ndiscr = 100, default = FALSE, clip = "on",
                      reverse = "none") {
 
-  if (is.waiver(label_graticule) && is.waiver(label_axes)) {
+  if (is_waiver(label_graticule) && is_waiver(label_axes)) {
     # if both `label_graticule` and `label_axes` are set to waive then we
     # use the default of labels on the left and at the bottom
     label_graticule <- ""
@@ -641,13 +641,13 @@ sf_breaks <- function(scale_x, scale_y, bbox, crs) {
       bbox[is.na(bbox)] <- c(-180, -90, 180, 90)[is.na(bbox)]
     }
 
-    if (!(is.waiver(scale_x$breaks) && is.null(scale_x$n.breaks))) {
+    if (!(is_waiver(scale_x$breaks) && is.null(scale_x$n.breaks))) {
       x_breaks <- scale_x$get_breaks(limits = bbox[c(1, 3)])
       finite <- is.finite(x_breaks)
       x_breaks <- if (any(finite)) x_breaks[finite] else NULL
     }
 
-    if (!(is.waiver(scale_y$breaks) && is.null(scale_y$n.breaks))) {
+    if (!(is_waiver(scale_y$breaks) && is.null(scale_y$n.breaks))) {
       y_breaks <- scale_y$get_breaks(limits = bbox[c(2, 4)])
       finite <- is.finite(y_breaks)
       y_breaks <- if (any(finite)) y_breaks[finite] else NULL
@@ -770,7 +770,7 @@ view_scales_from_graticule <- function(graticule, scale, aesthetic,
   if (scale$position != position) {
     # Try to use secondary axis' guide
     guide <- scale$secondary.axis$guide %||% waiver()
-    if (is.derived(guide)) {
+    if (is_derived(guide)) {
       guide <- scale$guide
     }
   } else {
diff --git a/R/facet-grid-.R b/R/facet-grid-.R
index 21d3fed9bd..0c0df60bb0 100644
--- a/R/facet-grid-.R
+++ b/R/facet-grid-.R
@@ -430,7 +430,7 @@ ulevels <- function(x, na.last = TRUE) {
 
 table_has_grob <- function(table, pattern) {
   grobs <- table$grobs[grep(pattern, table$layout$name)]
-  !all(vapply(grobs, is.zero, logical(1)))
+  !all(vapply(grobs, is_zero, logical(1)))
 }
 
 seam_table <- function(table, grobs = NULL, side, shift = 1, name, z = 1,
diff --git a/R/facet-null.R b/R/facet-null.R
index e2c4156aa6..860e5f3b84 100644
--- a/R/facet-null.R
+++ b/R/facet-null.R
@@ -30,9 +30,9 @@ FacetNull <- ggproto("FacetNull", Facet,
     layout_null()
   },
   map_data = function(data, layout, params) {
-    # Need the is.waiver check for special case where no data, but aesthetics
+    # Need the is_waiver check for special case where no data, but aesthetics
     # are mapped to vectors
-    if (is.waiver(data))
+    if (is_waiver(data))
       return(data_frame0(PANEL = factor()))
 
     if (empty(data))
diff --git a/R/facet-wrap.R b/R/facet-wrap.R
index 04ac484343..9345fc8a9d 100644
--- a/R/facet-wrap.R
+++ b/R/facet-wrap.R
@@ -327,7 +327,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     if (length(empty_bottom) > 0) {
       x_axes <- original$x$bottom[matched[empty_bottom]]
       clash["bottom"] <- strip == "bottom" && !inside && !free$x &&
-        !all(vapply(x_axes, is.zero, logical(1)))
+        !all(vapply(x_axes, is_zero, logical(1)))
       if (!clash["bottom"]) {
         bottom[empty_bottom] <- x_axes
       }
@@ -336,7 +336,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     if (length(empty_top) > 0) {
       x_axes <- original$x$top[matched[empty_top]]
       clash["top"] <- strip == "top" && !inside && !free$x &&
-        !all(vapply(x_axes, is.zero, logical(1)))
+        !all(vapply(x_axes, is_zero, logical(1)))
       if (!clash["top"]) {
         top[empty_top] <- x_axes
       }
@@ -345,7 +345,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     if (length(empty_right) > 0) {
       y_axes <- original$y$right[matched[empty_right]]
       clash["right"]  <- strip == "right" && !inside && !free$y &&
-        !all(vapply(y_axes, is.zero, logical(1)))
+        !all(vapply(y_axes, is_zero, logical(1)))
       if (!clash["right"]) {
         right[empty_right] <- y_axes
       }
@@ -354,7 +354,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
     if (length(empty_left) > 0) {
       y_axes <- original$y$left[matched[empty_left]]
       clash["left"]  <- strip == "left" && !inside && !free$y &&
-        !all(vapply(y_axes, is.zero, logical(1)))
+        !all(vapply(y_axes, is_zero, logical(1)))
       if (!clash["left"]) {
         left[empty_left] <- y_axes
       }
@@ -410,7 +410,7 @@ FacetWrap <- ggproto("FacetWrap", Facet,
 
     if (!inside) {
       axes  <- grepl(paste0("axis-", pos), table$layout$name)
-      has_axes <- !vapply(table$grobs[axes], is.zero, logical(1))
+      has_axes <- !vapply(table$grobs[axes], is_zero, logical(1))
       has_axes <- split(has_axes, table$layout[[pos]][axes])
       has_axes <- vapply(has_axes, sum, numeric(1)) > 0
       padding  <- rep(padding, length(has_axes))
diff --git a/R/grob-null.R b/R/grob-null.R
index 217c5a7560..da32009b3b 100644
--- a/R/grob-null.R
+++ b/R/grob-null.R
@@ -23,4 +23,4 @@ grobHeight.zeroGrob <- function(x) unit(0, "cm")
 #' @method drawDetails zeroGrob
 drawDetails.zeroGrob <- function(x, recording) {}
 
-is.zero <- function(x) is.null(x) || inherits(x, "zeroGrob")
+is_zero <- function(x) is.null(x) || inherits(x, "zeroGrob")
diff --git a/R/grouping.R b/R/grouping.R
index 80b9d18121..7db4807a0f 100644
--- a/R/grouping.R
+++ b/R/grouping.R
@@ -12,7 +12,7 @@ add_group <- function(data) {
   if (empty(data)) return(data)
 
   if (is.null(data[["group"]])) {
-    disc <- vapply(data, is.discrete, logical(1))
+    disc <- vapply(data, is_discrete, logical(1))
     disc[names(disc) %in% c("label", "PANEL")] <- FALSE
 
     if (any(disc)) {
diff --git a/R/guide-.R b/R/guide-.R
index 63bdedfb87..fe3a65bbca 100644
--- a/R/guide-.R
+++ b/R/guide-.R
@@ -920,7 +920,7 @@ Guide <- ggproto(
   #'
   #' The `gtable` argument with added title.
   add_title = function(gtable, title, position, just) {
-    if (is.zero(title)) {
+    if (is_zero(title)) {
       return(gtable)
     }
 
diff --git a/R/guide-axis-logticks.R b/R/guide-axis-logticks.R
index 5ca6552967..42caad3ce5 100644
--- a/R/guide-axis-logticks.R
+++ b/R/guide-axis-logticks.R
@@ -108,7 +108,7 @@ guide_axis_logticks <- function(
   if (is_bare_numeric(mid))    mid  <- rel(mid)
   if (is_bare_numeric(short)) short <- rel(short)
 
-  check_fun <- function(x) (is.rel(x) || is.unit(x)) && length(x) == 1
+  check_fun <- function(x) (is_rel(x) || is.unit(x)) && length(x) == 1
   what <- "a {.cls rel} or {.cls unit} object of length 1"
   check_object(long,  check_fun, what)
   check_object(mid,   check_fun, what)
diff --git a/R/guide-axis-stack.R b/R/guide-axis-stack.R
index effa6a5eaf..8a3ba4c91c 100644
--- a/R/guide-axis-stack.R
+++ b/R/guide-axis-stack.R
@@ -195,7 +195,7 @@ GuideAxisStack <- ggproto(
     }
 
     # Remove empty grobs
-    grobs <- grobs[!vapply(grobs, is.zero, logical(1))]
+    grobs <- grobs[!vapply(grobs, is_zero, logical(1))]
     if (length(grobs) == 0) {
       return(zeroGrob())
     }
diff --git a/R/guide-axis-theta.R b/R/guide-axis-theta.R
index 8abd11bce1..e5c12e6cd8 100644
--- a/R/guide-axis-theta.R
+++ b/R/guide-axis-theta.R
@@ -184,7 +184,7 @@ GuideAxisTheta <- ggproto(
 
   build_labels = function(key, elements, params) {
 
-    if (inherits(elements$text, "element_blank")) {
+    if (is_theme_element(elements$text, "blank")) {
       return(zeroGrob())
     }
 
@@ -197,7 +197,7 @@ GuideAxisTheta <- ggproto(
     }
 
     # Resolve text angle
-    if (is.waiver(params$angle) || is.null(params$angle)) {
+    if (is_waiver(params$angle) || is.null(params$angle)) {
       angle <- elements$text$angle
     } else {
       angle <- flip_text_angle(params$angle - rad2deg(key$theta))
@@ -268,12 +268,12 @@ GuideAxisTheta <- ggproto(
     key <- params$key
     key <- vec_slice(key, !is.na(key$.label) & nzchar(key$.label))
     labels <- validate_labels(key$.label)
-    if (length(labels) == 0 || inherits(elements$text, "element_blank")) {
+    if (length(labels) == 0 || is_theme_element(elements$text, "blank")) {
       return(list(offset = offset))
     }
 
     # Resolve text angle
-    if (is.waiver(params$angle %||% waiver())) {
+    if (is_waiver(params$angle %||% waiver())) {
       angle <- elements$text$angle
     } else {
       angle <- flip_text_angle(params$angle - rad2deg(key$theta))
@@ -365,7 +365,7 @@ GuideAxisTheta <- ggproto(
 
 theta_tickmarks <- function(key, element, length, offset = NULL) {
   n_breaks <- nrow(key)
-  if (n_breaks < 1 || inherits(element, "element_blank")) {
+  if (n_breaks < 1 || is_theme_element(element, "blank")) {
     return(zeroGrob())
   }
 
diff --git a/R/guide-axis.R b/R/guide-axis.R
index 53121bbc12..ae1784236f 100644
--- a/R/guide-axis.R
+++ b/R/guide-axis.R
@@ -263,10 +263,10 @@ GuideAxis <- ggproto(
   override_elements = function(params, elements, theme) {
     elements$text <-
       label_angle_heuristic(elements$text, params$position, params$angle)
-    if (inherits(elements$ticks, "element_blank")) {
+    if (is_theme_element(elements$ticks, "blank")) {
       elements$major_length <- unit(0, "cm")
     }
-    if (inherits(elements$minor, "element_blank") || isFALSE(params$minor.ticks)) {
+    if (is_theme_element(elements$minor, "blank") || isFALSE(params$minor.ticks)) {
       elements$minor_length <- unit(0, "cm")
     }
     return(elements)
@@ -383,7 +383,7 @@ GuideAxis <- ggproto(
     # Ticks
     major_cm <- convertUnit(elements$major_length, "cm", valueOnly = TRUE)
     range <- range(0, major_cm)
-    if (params$minor.ticks && !inherits(elements$minor, "element_blank")) {
+    if (params$minor.ticks && !is_theme_element(elements$minor, "blank")) {
       minor_cm <- convertUnit(elements$minor_length, "cm", valueOnly = TRUE)
       range <- range(range, minor_cm)
     }
@@ -424,7 +424,7 @@ GuideAxis <- ggproto(
     # Unlist the 'label' grobs
     z <- if (params$position == "left") c(2, 1, 3) else 1:3
     z <- rep(z, c(1, length(grobs$labels), 1))
-    has_labels <- !is.zero(grobs$labels[[1]])
+    has_labels <- !is_zero(grobs$labels[[1]])
     grobs  <- c(list(grobs$ticks), grobs$labels, list(grobs$title))
 
     # Initialise empty gtable
@@ -594,7 +594,7 @@ axis_label_priority_between <- function(x, y) {
 #'   overridden from the user- or theme-supplied element.
 #' @noRd
 label_angle_heuristic <- function(element, position, angle) {
-  if (!inherits(element, "element_text")
+  if (!is_theme_element(element, "text")
       || is.null(position)
       || is.null(angle %|W|% NULL)) {
     return(element)
diff --git a/R/guide-bins.R b/R/guide-bins.R
index d8fed79e42..d62d7af67b 100644
--- a/R/guide-bins.R
+++ b/R/guide-bins.R
@@ -341,7 +341,7 @@ GuideBins <- ggproto(
 
 parse_binned_breaks <- function(scale, breaks = scale$get_breaks()) {
 
-  if (is.waiver(scale$labels) || is.function(scale$labels)) {
+  if (is_waiver(scale$labels) || is.function(scale$labels)) {
     breaks <- breaks[!is.na(breaks)]
   }
   if (length(breaks) == 0) {
diff --git a/R/guide-custom.R b/R/guide-custom.R
index 12bd9705ad..c16260265e 100644
--- a/R/guide-custom.R
+++ b/R/guide-custom.R
@@ -96,7 +96,7 @@ GuideCustom <- ggproto(
     # Render title
     params <- replace_null(params, position = position, direction = direction)
     elems <- GuideLegend$setup_elements(params, self$elements, theme)
-    if (!is.waiver(params$title) && !is.null(params$title)) {
+    if (!is_waiver(params$title) && !is.null(params$title)) {
       title <- self$build_title(params$title, elems, params)
     } else {
       title <- zeroGrob()
diff --git a/R/guide-legend.R b/R/guide-legend.R
index 5fb85d3a95..884b59cbf8 100644
--- a/R/guide-legend.R
+++ b/R/guide-legend.R
@@ -545,7 +545,7 @@ GuideLegend <- ggproto(
     gt <- gtable(widths = widths, heights = heights)
 
     # Add keys
-    if (!is.zero(grobs$decor)) {
+    if (!is_zero(grobs$decor)) {
       n_key_layers <- params$n_key_layers %||% 1L
       key_cols <- rep(layout$key_col, each = n_key_layers)
       key_rows <- rep(layout$key_row, each = n_key_layers)
@@ -561,7 +561,7 @@ GuideLegend <- ggproto(
       )
     }
 
-    if (!is.zero(grobs$labels)) {
+    if (!is_zero(grobs$labels)) {
       gt <- gtable_add_grob(
         gt, grobs$labels,
         name = names(labels) %||%
@@ -580,7 +580,7 @@ GuideLegend <- ggproto(
     gt <- gtable_add_padding(gt, unit(elements$padding, "cm"))
 
     # Add background
-    if (!is.zero(elements$background)) {
+    if (!is_zero(elements$background)) {
       gt <- gtable_add_grob(
         gt, elements$background,
         name = "background", clip = "off",
@@ -648,7 +648,7 @@ set_key_size <- function(key, linewidth = NULL, size = NULL, default = NULL) {
 keep_key_data <- function(key, data, aes, show) {
   # First, can we exclude based on anything else than actually checking the
   # data that we should include or drop the key?
-  if (!is.discrete(key$.value)) {
+  if (!is_discrete(key$.value)) {
     return(TRUE)
   }
   if (is_named(show)) {
diff --git a/R/guides-.R b/R/guides-.R
index d96ef16074..2f7cd6d317 100644
--- a/R/guides-.R
+++ b/R/guides-.R
@@ -492,7 +492,7 @@ Guides <- ggproto(
     )
 
     grobs <- self$draw(theme, positions, theme$legend.direction)
-    keep <- !vapply(grobs, is.zero, logical(1), USE.NAMES = FALSE)
+    keep <- !vapply(grobs, is_zero, logical(1), USE.NAMES = FALSE)
     grobs <- grobs[keep]
     if (length(grobs) < 1) {
       return(zeroGrob())
@@ -590,7 +590,7 @@ Guides <- ggproto(
   # arguments to collect guides
   package_box = function(grobs, position, theme) {
 
-    if (is.zero(grobs) || length(grobs) == 0) {
+    if (is_zero(grobs) || length(grobs) == 0) {
       return(zeroGrob())
     }
 
diff --git a/R/guides-grid.R b/R/guides-grid.R
index 1b2f1a4a99..9e70adaf37 100644
--- a/R/guides-grid.R
+++ b/R/guides-grid.R
@@ -30,7 +30,7 @@ guide_grid <- function(theme, panel_params, coord, square = TRUE) {
   grill <- compact(grill)
 
   background <- element_render(theme, "panel.background")
-  if (!isTRUE(square) && !is.zero(background)) {
+  if (!isTRUE(square) && !is_zero(background)) {
     gp <- background$gp
     background <- data_frame0(x = c(1, 1, -1, -1), y = c(1, -1, -1, 1)) * Inf
     background <- coord_munch(coord, background, panel_params, is_closed = TRUE)
diff --git a/R/labeller.R b/R/labeller.R
index 9afd572da0..6d3c1b10ae 100644
--- a/R/labeller.R
+++ b/R/labeller.R
@@ -296,7 +296,7 @@ as_labeller <- function(x, default = label_value, multi_line = TRUE) {
       x(labels)
     } else if (is.function(x)) {
       default(lapply(labels, x))
-    } else if (is.formula(x)) {
+    } else if (is_formula(x)) {
       default(lapply(labels, as_function(x)))
     } else if (is.character(x)) {
       default(lapply(labels, function(label) x[label]))
@@ -546,7 +546,7 @@ build_strip <- function(label_df, labeller, theme, horizontal) {
 #'
 #' @noRd
 assemble_strips <- function(grobs, theme, horizontal = TRUE, clip) {
-  if (length(grobs) == 0 || is.zero(grobs[[1]])) {
+  if (length(grobs) == 0 || is_zero(grobs[[1]])) {
     # Subsets matrix of zeroGrobs to correct length (#4050)
     grobs <- grobs[seq_len(NROW(grobs))]
     return(grobs)
diff --git a/R/labels.R b/R/labels.R
index 27c1e96de6..17374aafbd 100644
--- a/R/labels.R
+++ b/R/labels.R
@@ -189,7 +189,7 @@ labs <- function(..., title = waiver(), subtitle = waiver(), caption = waiver(),
     tag = tag, alt = allow_lambda(alt), alt_insight = alt_insight,
     dictionary = dictionary, .ignore_empty = "all")
 
-  is_waive <- vapply(args, is.waiver, logical(1))
+  is_waive <- vapply(args, is_waiver, logical(1))
   args <- args[!is_waive]
   # remove duplicated arguments
   args <- args[!duplicated(names(args))]
diff --git a/R/layer.R b/R/layer.R
index 171dc4631e..0fdeed5a5c 100644
--- a/R/layer.R
+++ b/R/layer.R
@@ -446,7 +446,7 @@ Layer <- ggproto("Layer", NULL,
   #'
   #' A data frame with layer data or `NULL`
   layer_data = function(self, plot_data) {
-    if (is.waiver(self$data)) {
+    if (is_waiver(self$data)) {
       data <- plot_data
     } else if (is.function(self$data)) {
       data <- self$data(plot_data)
@@ -456,7 +456,7 @@ Layer <- ggproto("Layer", NULL,
     } else {
       data <- self$data
     }
-    if (is.null(data) || is.waiver(data)) data else unrowname(data)
+    if (is.null(data) || is_waiver(data)) data else unrowname(data)
   },
 
   #' @field setup_layer
diff --git a/R/layout.R b/R/layout.R
index 88fa8185a3..3149c2ec74 100644
--- a/R/layout.R
+++ b/R/layout.R
@@ -498,7 +498,7 @@ Layout <- ggproto(
 
     primary   <- scale$make_title(prim_guide, prim_scale, prim_label)
     secondary <- scale$make_sec_title(seco_guide, seco_scale, seco_label)
-    if (is.derived(secondary)) {
+    if (is_derived(secondary)) {
       secondary <- primary
     }
 
@@ -537,7 +537,7 @@ Layout <- ggproto(
         } else {
           switch(label, x = ".bottom", y = ".right")
         }
-        if (is.null(labels[[label]][[i]]) || is.waiver(labels[[label]][[i]]))
+        if (is.null(labels[[label]][[i]]) || is_waiver(labels[[label]][[i]]))
           return(zeroGrob())
 
         element_render(
diff --git a/R/plot-build.R b/R/plot-build.R
index 24644951c2..9cd01b54d5 100644
--- a/R/plot-build.R
+++ b/R/plot-build.R
@@ -348,7 +348,7 @@ table_add_tag <- function(table, label, theme) {
     return(table)
   }
   element <- calc_element("plot.tag", theme)
-  if (inherits(element, "element_blank")) {
+  if (is_theme_element(element, "blank")) {
     return(table)
   }
 
@@ -454,7 +454,7 @@ table_add_tag <- function(table, label, theme) {
 # Add the legends to the gtable
 table_add_legends <- function(table, legends, theme) {
 
-  if (is.zero(legends)) {
+  if (is_zero(legends)) {
     legends <- rep(list(zeroGrob()), 5)
     names(legends) <- c(.trbl, "inside")
   }
@@ -465,7 +465,7 @@ table_add_legends <- function(table, legends, theme) {
     names(legends)
   )
 
-  empty <- vapply(legends, is.zero, logical(1))
+  empty <- vapply(legends, is_zero, logical(1))
   widths[!empty]  <- lapply(legends[!empty], gtable_width)
   heights[!empty] <- lapply(legends[!empty], gtable_height)
   spacing <- calc_element("legend.box.spacing", theme) %||% unit(0.2, "cm")
diff --git a/R/quick-plot.R b/R/quick-plot.R
index 64e2ab460d..4dfa478be3 100644
--- a/R/quick-plot.R
+++ b/R/quick-plot.R
@@ -121,7 +121,7 @@ qplot <- function(x, y, ..., data, facets = NULL, margins = FALSE,
       geom[geom == "auto"] <- "qq"
     } else if (missing(y)) {
       x <- eval_tidy(mapping$x, data, caller_env)
-      if (is.discrete(x)) {
+      if (is_discrete(x)) {
         geom[geom == "auto"] <- "bar"
       } else {
         geom[geom == "auto"] <- "histogram"
@@ -139,7 +139,7 @@ qplot <- function(x, y, ..., data, facets = NULL, margins = FALSE,
 
   if (is.null(facets)) {
     p <- p + facet_null()
-  } else if (is.formula(facets) && length(facets) == 2) {
+  } else if (is_formula(facets) && length(facets) == 2) {
     p <- p + facet_wrap(facets)
   } else {
     p <- p + facet_grid(rows = deparse(facets), margins = margins)
diff --git a/R/scale-.R b/R/scale-.R
index cf169cd19e..77d01f6bad 100644
--- a/R/scale-.R
+++ b/R/scale-.R
@@ -228,7 +228,7 @@ discrete_scale <- function(aesthetics, scale_name = deprecated(), palette, name
   labels <- allow_lambda(labels)
   minor_breaks <- allow_lambda(minor_breaks)
 
-  if (!is.function(limits) && (length(limits) > 0) && !is.discrete(limits)) {
+  if (!is.function(limits) && (length(limits) > 0) && !is_discrete(limits)) {
     cli::cli_warn(c(
       "Continuous limits supplied to discrete scale.",
       "i" = "Did you mean {.code limits = factor(...)} or {.fn scale_*_continuous}?"
@@ -1117,7 +1117,7 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
     b <- b[is.finite(b)]
 
     transformation <- self$get_transformation()
-    if (is.waiver(self$minor_breaks)) {
+    if (is_waiver(self$minor_breaks)) {
       if (is.null(b)) {
         breaks <- NULL
       } else {
@@ -1164,7 +1164,7 @@ ScaleContinuous <- ggproto("ScaleContinuous", Scale,
       )
     }
 
-    if (is.waiver(self$labels)) {
+    if (is_waiver(self$labels)) {
       labels <- transformation$format(breaks)
     } else if (is.function(self$labels)) {
       labels <- self$labels(breaks)
@@ -1338,7 +1338,7 @@ ScaleDiscrete <- ggproto("ScaleDiscrete", Scale,
       return(NULL)
     }
 
-    if (is.waiver(self$breaks)) {
+    if (is_waiver(self$breaks)) {
       breaks <- limits
     } else if (is.function(self$breaks)) {
       breaks <- self$breaks(limits)
@@ -1402,7 +1402,7 @@ ScaleDiscrete <- ggproto("ScaleDiscrete", Scale,
       )
     }
 
-    if (is.waiver(labels)) {
+    if (is_waiver(labels)) {
       if (!is.null(names(breaks))) {
         labels <- names(breaks)
       } else if (is.numeric(breaks)) {
@@ -1554,7 +1554,7 @@ ScaleBinned <- ggproto("ScaleBinned", Scale,
 
     if (is.null(self$breaks)) {
       return(NULL)
-    } else if (is.waiver(self$breaks)) {
+    } else if (is_waiver(self$breaks)) {
       if (self$nice.breaks) {
         if (!is.null(self$n.breaks) && support_nbreaks(transformation$breaks)) {
           breaks <- transformation$breaks(limits, n = self$n.breaks)
@@ -1656,7 +1656,7 @@ ScaleBinned <- ggproto("ScaleBinned", Scale,
         "Invalid {.arg labels} specification. Use {.code NULL}, not {.code NA}.",
         call = self$call
       )
-    } else if (is.waiver(self$labels)) {
+    } else if (is_waiver(self$labels)) {
       labels <- transformation$format(breaks)
     } else if (is.function(self$labels)) {
       labels <- self$labels(breaks)
diff --git a/R/scale-continuous.R b/R/scale-continuous.R
index 14d7c8e725..8da2f94428 100644
--- a/R/scale-continuous.R
+++ b/R/scale-continuous.R
@@ -149,21 +149,21 @@ ScaleContinuousPosition <- ggproto("ScaleContinuousPosition", ScaleContinuous,
   },
   break_info = function(self, range = NULL) {
     breaks <- ggproto_parent(ScaleContinuous, self)$break_info(range)
-    if (!(is.waiver(self$secondary.axis) || self$secondary.axis$empty())) {
+    if (!(is_waiver(self$secondary.axis) || self$secondary.axis$empty())) {
       self$secondary.axis$init(self)
       breaks <- c(breaks, self$secondary.axis$break_info(breaks$range, self))
     }
     breaks
   },
   sec_name = function(self) {
-    if (is.waiver(self$secondary.axis)) {
+    if (is_waiver(self$secondary.axis)) {
       waiver()
     } else {
       self$secondary.axis$name
     }
   },
   make_sec_title = function(self, ...) {
-    if (!is.waiver(self$secondary.axis)) {
+    if (!is_waiver(self$secondary.axis)) {
       self$secondary.axis$make_title(...)
     } else {
       ggproto_parent(ScaleContinuous, self)$make_sec_title(...)
diff --git a/R/scale-date.R b/R/scale-date.R
index 249bf891f8..3e3eda8a0e 100644
--- a/R/scale-date.R
+++ b/R/scale-date.R
@@ -318,15 +318,15 @@ datetime_scale <- function(aesthetics, transform, trans = deprecated(),
   if (is.character(breaks)) breaks <- breaks_width(breaks)
   if (is.character(minor_breaks)) minor_breaks <- breaks_width(minor_breaks)
 
-  if (!is.waiver(date_breaks)) {
+  if (!is_waiver(date_breaks)) {
     check_string(date_breaks)
     breaks <- breaks_width(date_breaks)
   }
-  if (!is.waiver(date_minor_breaks)) {
+  if (!is_waiver(date_minor_breaks)) {
     check_string(date_minor_breaks)
     minor_breaks <- breaks_width(date_minor_breaks)
   }
-  if (!is.waiver(date_labels)) {
+  if (!is_waiver(date_labels)) {
     check_string(date_labels)
     if (transform == "hms") {
       labels <- label_time(date_labels)
@@ -404,21 +404,21 @@ ScaleContinuousDatetime <- ggproto("ScaleContinuousDatetime", ScaleContinuous,
   },
   break_info = function(self, range = NULL) {
     breaks <- ggproto_parent(ScaleContinuous, self)$break_info(range)
-    if (!(is.waiver(self$secondary.axis) || self$secondary.axis$empty())) {
+    if (!(is_waiver(self$secondary.axis) || self$secondary.axis$empty())) {
       self$secondary.axis$init(self)
       breaks <- c(breaks, self$secondary.axis$break_info(breaks$range, self))
     }
     breaks
   },
   sec_name = function(self) {
-    if (is.waiver(self$secondary.axis)) {
+    if (is_waiver(self$secondary.axis)) {
       waiver()
     } else {
       self$secondary.axis$name
     }
   },
   make_sec_title = function(self, ...) {
-    if (!is.waiver(self$secondary.axis)) {
+    if (!is_waiver(self$secondary.axis)) {
       self$secondary.axis$make_title(...)
     } else {
       ggproto_parent(ScaleContinuous, self)$make_sec_title(...)
@@ -458,21 +458,21 @@ ScaleContinuousDate <- ggproto("ScaleContinuousDate", ScaleContinuous,
   },
   break_info = function(self, range = NULL) {
     breaks <- ggproto_parent(ScaleContinuous, self)$break_info(range)
-    if (!(is.waiver(self$secondary.axis) || self$secondary.axis$empty())) {
+    if (!(is_waiver(self$secondary.axis) || self$secondary.axis$empty())) {
       self$secondary.axis$init(self)
       breaks <- c(breaks, self$secondary.axis$break_info(breaks$range, self))
     }
     breaks
   },
   sec_name = function(self) {
-    if (is.waiver(self$secondary.axis)) {
+    if (is_waiver(self$secondary.axis)) {
       waiver()
     } else {
       self$secondary.axis$name
     }
   },
   make_sec_title = function(self, ...) {
-    if (!is.waiver(self$secondary.axis)) {
+    if (!is_waiver(self$secondary.axis)) {
       self$secondary.axis$make_title(...)
     } else {
       ggproto_parent(ScaleContinuous, self)$make_sec_title(...)
diff --git a/R/scale-discrete-.R b/R/scale-discrete-.R
index ce1dd893d5..680167b060 100644
--- a/R/scale-discrete-.R
+++ b/R/scale-discrete-.R
@@ -119,7 +119,7 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
   continuous_limits = NULL,
 
   train = function(self, x) {
-    if (is.discrete(x)) {
+    if (is_discrete(x)) {
       self$range$train(x, drop = self$drop, na.rm = !self$na.translate)
     } else {
       self$range_c$train(x)
@@ -156,7 +156,7 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
     if (inherits(x, "AsIs")) {
       return(x)
     }
-    if (is.discrete(x)) {
+    if (is_discrete(x)) {
       values <- self$palette(length(limits))
       if (!is.numeric(values)) {
         cli::cli_abort(
@@ -185,7 +185,7 @@ ScaleDiscretePosition <- ggproto("ScaleDiscretePosition", ScaleDiscrete,
   },
 
   sec_name = function(self) {
-    if (is.waiver(self$secondary.axis)) {
+    if (is_waiver(self$secondary.axis)) {
       waiver()
     } else {
       self$secondary.axis$name
diff --git a/R/scale-expansion.R b/R/scale-expansion.R
index 9c682eeaa6..89b8bd06ad 100644
--- a/R/scale-expansion.R
+++ b/R/scale-expansion.R
@@ -228,7 +228,7 @@ expand_limits_discrete_trans <- function(limits, expand = expansion(0, 0),
                                          range_continuous = NULL) {
   discrete_limits <- NULL
   if (length(limits) > 0) {
-    if (is.discrete(limits)) {
+    if (is_discrete(limits)) {
       discrete_limits <- c(1, length(limits)) # for backward compatibility
     } else {
       discrete_limits <- range(limits)
diff --git a/R/scale-manual.R b/R/scale-manual.R
index 9f6284361b..87b479e926 100644
--- a/R/scale-manual.R
+++ b/R/scale-manual.R
@@ -171,7 +171,7 @@ manual_scale <- function(aesthetic, values = NULL, breaks = waiver(),
   }
 
   # order values according to breaks
-  if (is.vector(values) && is.null(names(values)) && !is.waiver(breaks) &&
+  if (is.vector(values) && is.null(names(values)) && !is_waiver(breaks) &&
       !is.null(breaks) && !is.function(breaks)) {
     if (length(breaks) <= length(values)) {
       names(values) <- breaks
diff --git a/R/scale-view.R b/R/scale-view.R
index a926084cd8..db0b4bcd65 100644
--- a/R/scale-view.R
+++ b/R/scale-view.R
@@ -45,7 +45,7 @@ view_scale_primary <- function(scale, limits = scale$get_limits(),
 view_scale_secondary <- function(scale, limits = scale$get_limits(),
                                  continuous_range = scale$dimension(limits = limits)) {
 
-  if (is.null(scale$secondary.axis) || is.waiver(scale$secondary.axis) || scale$secondary.axis$empty()) {
+  if (is.null(scale$secondary.axis) || is_waiver(scale$secondary.axis) || scale$secondary.axis$empty()) {
     # if there is no second axis, return the primary scale with no guide
     # this guide can be overridden using guides()
     primary_scale <- view_scale_primary(scale, limits, continuous_range)
diff --git a/R/stat-function.R b/R/stat-function.R
index 8ea365b708..d0cd7ec512 100644
--- a/R/stat-function.R
+++ b/R/stat-function.R
@@ -70,7 +70,7 @@ StatFunction <- ggproto("StatFunction", Stat,
       }
     }
 
-    if (is.formula(fun)) fun <- as_function(fun)
+    if (is_formula(fun)) fun <- as_function(fun)
 
     y_out <- inject(fun(x_trans, !!!args))
     if (!is.null(scales$y) && !scales$y$is_discrete()) {
diff --git a/R/theme-elements.R b/R/theme-elements.R
index 0ab5930dd0..3d367c6da7 100644
--- a/R/theme-elements.R
+++ b/R/theme-elements.R
@@ -178,25 +178,6 @@ element_text <- function(family = NULL, face = NULL, colour = NULL,
   )
 }
 
-#' @export
-#' @param type For testing elements: the type of element to expect. One of
-#'   `"blank"`, `"rect"`, `"line"` or `"text"`.
-#' @rdname is_tests
-is_theme_element <- function(x, type = "any") {
-  switch(
-    type %||% "any",
-    any   = inherits(x, "element"),
-    rect  = inherits(x, "element_rect"),
-    line  = inherits(x, "element_line"),
-    text  = inherits(x, "element_text"),
-    blank = inherits(x, "element_blank"),
-    # TODO: ideally we accept more elements from extensions. We need to
-    # consider how this will work with S7 classes, where ggplot2 doesn't know
-    # about the extension's class objects.
-    FALSE
-  )
-}
-
 #' @export
 #' @rdname element
 element_polygon <- function(fill = NULL, colour = NULL, linewidth = NULL,
@@ -272,6 +253,26 @@ element_geom <- function(
   fill = NULL, colour = NULL
 )
 
+#' @export
+#' @param type For testing elements: the type of element to expect. One of
+#'   `"blank"`, `"rect"`, `"line"`, `"text"`, `"polygon"`, `"point"` or `"geom"`.
+#' @rdname is_tests
+is_theme_element <- function(x, type = "any") {
+  switch(
+    type %||% "any",
+    any     = inherits(x, "element"),
+    rect    = inherits(x, "element_rect"),
+    line    = inherits(x, "element_line"),
+    text    = inherits(x, "element_text"),
+    polygon = inherits(x, "element_polygon"),
+    point   = inherits(x, "element_point"),
+    geom    = inherits(x, "element_geom"),
+    blank   = inherits(x, "element_blank"),
+    # We don't consider elements from extensions
+    FALSE
+  )
+}
+
 #' @export
 print.element <- function(x, ...) utils::str(x)
 
@@ -289,7 +290,7 @@ print.rel <- function(x, ...) print(noquote(paste(x, " *", sep = "")))
 #' Reports whether x is a rel object
 #' @param x An object to test
 #' @keywords internal
-is.rel <- function(x) inherits(x, "rel")
+is_rel <- function(x) inherits(x, "rel")
 
 #' Render a specified theme element into a grob
 #'
@@ -853,7 +854,7 @@ check_element <- function(el, elname, element_tree, call = caller_env()) {
   if ("margin" %in% eldef$class) {
     if (!is.unit(el) && length(el) == 4)
       cli::cli_abort("The {.var {elname}} theme element must be a {.cls unit} vector of length 4.", call = call)
-  } else if (!inherits(el, eldef$class) && !inherits(el, "element_blank")) {
+  } else if (!inherits(el, eldef$class) && !is_theme_element(el, "blank")) {
     cli::cli_abort("The {.var {elname}} theme element must be a {.cls {eldef$class}} object.", call = call)
   }
   invisible()
diff --git a/R/theme.R b/R/theme.R
index 8ad12765a0..61f6bf75be 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -917,9 +917,9 @@ combine_elements <- function(e1, e2) {
   }
 
   # Inheritance of rel objects
-  if (is.rel(e1)) {
+  if (is_rel(e1)) {
     # Both e1 and e2 are rel, give product as another rel
-    if (is.rel(e2)) {
+    if (is_rel(e2)) {
       return(rel(unclass(e1) * unclass(e2)))
     }
     # If e2 is a unit/numeric, return modified unit/numeric
@@ -959,12 +959,12 @@ combine_elements <- function(e1, e2) {
   e1[n] <- e2[n]
 
   # Calculate relative sizes
-  if (is.rel(e1$size)) {
+  if (is_rel(e1$size)) {
     e1$size <- e2$size * unclass(e1$size)
   }
 
   # Calculate relative linewidth
-  if (is.rel(e1$linewidth)) {
+  if (is_rel(e1$linewidth)) {
     e1$linewidth <- e2$linewidth * unclass(e1$linewidth)
   }
 
diff --git a/R/utilities.R b/R/utilities.R
index 8e6f9d46e9..d4fd0ccef4 100644
--- a/R/utilities.R
+++ b/R/utilities.R
@@ -12,7 +12,7 @@ scales::alpha
 }
 
 "%|W|%" <- function(a, b) {
-  if (!is.waiver(a)) a else b
+  if (!is_waiver(a)) a else b
 }
 
 # Check required aesthetics are present
@@ -183,7 +183,7 @@ should_stop <- function(expr) {
 #' calling function should just use the default value.  It is used in certain
 #' functions to distinguish between displaying nothing (`NULL`) and
 #' displaying a default value calculated elsewhere (`waiver()`).
-#' `is.waiver()` reports whether an object is a waiver.
+#' `is_waiver()` reports whether an object is a waiver.
 #'
 #' @export
 #' @keywords internal
@@ -192,7 +192,7 @@ waiver <- function() structure(list(), class = "waiver")
 #' @param x An object to test
 #' @export
 #' @rdname waiver
-is.waiver <- function(x) inherits(x, "waiver")
+is_waiver <- function(x) inherits(x, "waiver")
 
 pal_binned <- function(palette) {
   force(palette)
@@ -279,10 +279,10 @@ snake_class <- function(x) {
 }
 
 empty <- function(df) {
-  is.null(df) || nrow(df) == 0 || ncol(df) == 0 || is.waiver(df)
+  is.null(df) || nrow(df) == 0 || ncol(df) == 0 || is_waiver(df)
 }
 
-is.discrete <- function(x) {
+is_discrete <- function(x) {
   is.factor(x) || is.character(x) || is.logical(x)
 }
 
@@ -316,8 +316,6 @@ compact <- function(x) {
   x[!null]
 }
 
-is.formula <- function(x) inherits(x, "formula")
-
 dispatch_args <- function(f, ...) {
   args <- list(...)
   formals <- formals(f)
diff --git a/man/is.rel.Rd b/man/is_rel.Rd
similarity index 86%
rename from man/is.rel.Rd
rename to man/is_rel.Rd
index 67cda26b80..032e84f709 100644
--- a/man/is.rel.Rd
+++ b/man/is_rel.Rd
@@ -1,10 +1,10 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/theme-elements.R
-\name{is.rel}
-\alias{is.rel}
+\name{is_rel}
+\alias{is_rel}
 \title{Reports whether x is a rel object}
 \usage{
-is.rel(x)
+is_rel(x)
 }
 \arguments{
 \item{x}{An object to test}
diff --git a/man/is_tests.Rd b/man/is_tests.Rd
index bb0b25e799..b6a5c86da8 100644
--- a/man/is_tests.Rd
+++ b/man/is_tests.Rd
@@ -70,7 +70,7 @@ is.theme(x) # Deprecated
 \item{x}{An object to test}
 
 \item{type}{For testing elements: the type of element to expect. One of
-\code{"blank"}, \code{"rect"}, \code{"line"} or \code{"text"}.}
+\code{"blank"}, \code{"rect"}, \code{"line"}, \code{"text"}, \code{"polygon"}, \code{"point"} or \code{"geom"}.}
 }
 \description{
 Reports wether \code{x} is a type of object
diff --git a/man/waiver.Rd b/man/waiver.Rd
index 88fa06ba57..c1ecfe37bb 100644
--- a/man/waiver.Rd
+++ b/man/waiver.Rd
@@ -2,12 +2,12 @@
 % Please edit documentation in R/utilities.R
 \name{waiver}
 \alias{waiver}
-\alias{is.waiver}
+\alias{is_waiver}
 \title{A waiver object.}
 \usage{
 waiver()
 
-is.waiver(x)
+is_waiver(x)
 }
 \arguments{
 \item{x}{An object to test}
@@ -17,6 +17,6 @@ A waiver is a "flag" object, similar to \code{NULL}, that indicates the
 calling function should just use the default value.  It is used in certain
 functions to distinguish between displaying nothing (\code{NULL}) and
 displaying a default value calculated elsewhere (\code{waiver()}).
-\code{is.waiver()} reports whether an object is a waiver.
+\code{is_waiver()} reports whether an object is a waiver.
 }
 \keyword{internal}
diff --git a/tests/testthat/test-guide-legend.R b/tests/testthat/test-guide-legend.R
index cd2311ee93..de9fdb38ab 100644
--- a/tests/testthat/test-guide-legend.R
+++ b/tests/testthat/test-guide-legend.R
@@ -5,7 +5,7 @@ test_that("show.legend handles named vectors", {
     g <- ggplotGrob(p)
     gb <- grep("guide-box", g$layout$name)
     n <- vapply(g$grobs[gb], function(x) {
-      if (is.zero(x)) return(0)
+      if (is_zero(x)) return(0)
       length(x$grobs) - 1
     }, numeric(1))
     sum(n)
diff --git a/tests/testthat/test-guides.R b/tests/testthat/test-guides.R
index 1a3a31143a..64391776e3 100644
--- a/tests/testthat/test-guides.R
+++ b/tests/testthat/test-guides.R
@@ -159,7 +159,7 @@ test_that("empty guides are dropped", {
   guides <- p$plot$guides$assemble(theme_gray())
 
   # All guide-boxes should be empty
-  expect_true(is.zero(guides))
+  expect_true(is_zero(guides))
 })
 
 test_that("bins can be parsed by guides for all scale types", {