diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index 853092dd85e..c85064759ea 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -4376,7 +4376,7 @@ impl u8 {
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_uppercase(&self) -> u8 {
-        // Unset the fith bit if this is a lowercase letter
+        // Unset the fifth bit if this is a lowercase letter
         *self & !((self.is_ascii_lowercase() as u8) << 5)
     }
 
@@ -4399,7 +4399,7 @@ impl u8 {
     #[stable(feature = "ascii_methods_on_intrinsics", since = "1.23.0")]
     #[inline]
     pub fn to_ascii_lowercase(&self) -> u8 {
-        // Set the fith bit if this is an uppercase letter
+        // Set the fifth bit if this is an uppercase letter
         *self | ((self.is_ascii_uppercase() as u8) << 5)
     }