diff --git a/src/libstd/sys/redox/time.rs b/src/libstd/sys/redox/time.rs
index cf798500b7fd2..5c491115c5516 100644
--- a/src/libstd/sys/redox/time.rs
+++ b/src/libstd/sys/redox/time.rs
@@ -144,7 +144,7 @@ impl Instant {
 
     pub fn sub_instant(&self, other: &Instant) -> Duration {
         self.t.sub_timespec(&other.t).unwrap_or_else(|_| {
-            panic!("other was less than the current instant")
+            panic!("specified instant was later than self")
         })
     }
 
diff --git a/src/libstd/sys/unix/time.rs b/src/libstd/sys/unix/time.rs
index 8312793590993..89786eb2a6c48 100644
--- a/src/libstd/sys/unix/time.rs
+++ b/src/libstd/sys/unix/time.rs
@@ -289,7 +289,7 @@ mod inner {
 
         pub fn sub_instant(&self, other: &Instant) -> Duration {
             self.t.sub_timespec(&other.t).unwrap_or_else(|_| {
-                panic!("other was less than the current instant")
+                panic!("specified instant was later than self")
             })
         }