diff --git a/base/precompilation.jl b/base/precompilation.jl
index 4b7da84a17d55..a39563178632f 100644
--- a/base/precompilation.jl
+++ b/base/precompilation.jl
@@ -43,12 +43,12 @@ function ExplicitEnv(envpath::String=Base.active_project())
 
     # Collect all direct dependencies of the project
     for key in ["deps", "weakdeps", "extras"]
-        for (name, _uuid::String) in get(Dict{String, Any}, project_d, key)::Dict{String, Any}
+        for (name, _uuid) in get(Dict{String, Any}, project_d, key)::Dict{String, Any}
             v = key == "deps" ? project_deps :
                 key == "weakdeps" ? project_weakdeps :
                 key == "extras" ? project_extras :
                 error()
-            uuid = UUID(_uuid)
+            uuid = UUID(_uuid::String)
             v[name] = uuid
             names[UUID(uuid)] = name
             project_uuid_to_name[name] = UUID(uuid)
@@ -75,9 +75,11 @@ function ExplicitEnv(envpath::String=Base.active_project())
 
     project_extensions = Dict{String, Vector{UUID}}()
     # Collect all extensions of the project
-    for (name, triggers::Union{String, Vector{String}}) in get(Dict{String, Any}, project_d, "extensions")::Dict{String, Any}
+    for (name, triggers) in get(Dict{String, Any}, project_d, "extensions")::Dict{String, Any}
         if triggers isa String
             triggers = [triggers]
+        else
+            triggers = triggers::Vector{String}
         end
         uuids = UUID[]
         for trigger in triggers
@@ -107,8 +109,9 @@ function ExplicitEnv(envpath::String=Base.active_project())
     sizehint!(name_to_uuid, length(manifest_d))
     sizehint!(lookup_strategy, length(manifest_d))
 
-    for (name, pkg_infos::Vector{Any}) in get_deps(manifest_d)
-        for pkg_info::Dict{String, Any} in pkg_infos
+    for (name, pkg_infos) in get_deps(manifest_d)
+        for pkg_info in pkg_infos::Vector{Any}
+            pkg_info = pkg_info::Dict{String, Any}
             m_uuid = UUID(pkg_info["uuid"]::String)
 
             # If we have multiple packages with the same name we will overwrite things here
@@ -129,8 +132,8 @@ function ExplicitEnv(envpath::String=Base.active_project())
                 # Expanded format:
                 else
                     uuids = UUID[]
-                    for (name_dep, _dep_uuid::String) in deps_pkg
-                        dep_uuid = UUID(_dep_uuid)
+                    for (name_dep, _dep_uuid) in deps_pkg
+                        dep_uuid = UUID(_dep_uuid::String)
                         push!(uuids, dep_uuid)
                         names[dep_uuid] = name_dep
                     end
@@ -140,9 +143,11 @@ function ExplicitEnv(envpath::String=Base.active_project())
 
             # Extensions
             deps_pkg = get(Dict{String, Any}, pkg_info, "extensions")::Dict{String, Any}
-            for (ext, triggers::Union{String, Vector{String}}) in deps_pkg
+            for (ext, triggers) in deps_pkg
                 if triggers isa String
                     triggers = [triggers]
+                else
+                    triggers = triggers::Vector{String}
                 end
                 deps_pkg[ext] = triggers
             end
diff --git a/base/regex.jl b/base/regex.jl
index 38eb4cc512552..9444c9a9fb63e 100644
--- a/base/regex.jl
+++ b/base/regex.jl
@@ -28,7 +28,7 @@ mutable struct Regex <: AbstractPattern
 
     function Regex(pattern::AbstractString, compile_options::Integer,
                    match_options::Integer)
-        pattern = String(pattern)
+        pattern = String(pattern)::String
         compile_options = UInt32(compile_options)
         match_options = UInt32(match_options)
         if (compile_options & ~PCRE.COMPILE_MASK) != 0
diff --git a/stdlib/REPL/src/LineEdit.jl b/stdlib/REPL/src/LineEdit.jl
index c92dca8c8e015..e881a65ca6b1c 100644
--- a/stdlib/REPL/src/LineEdit.jl
+++ b/stdlib/REPL/src/LineEdit.jl
@@ -166,7 +166,7 @@ region_active(s::PromptState) = s.region_active
 region_active(s::ModeState) = :off
 
 
-input_string(s::PromptState) = String(take!(copy(s.input_buffer)))
+input_string(s::PromptState) = String(take!(copy(s.input_buffer)))::String
 
 input_string_newlines(s::PromptState) = count(c->(c == '\n'), input_string(s))
 function input_string_newlines_aftercursor(s::PromptState)