diff --git a/library/core/src/num/mod.rs b/library/core/src/num/mod.rs
index 1e7d75f9c265..6bacaccd24ac 100644
--- a/library/core/src/num/mod.rs
+++ b/library/core/src/num/mod.rs
@@ -228,7 +228,7 @@ impl u8 {
 
     /// Assumes self is ascii
     #[inline]
-    pub(crate) fn ascii_change_case_unchecked(&self) -> u8 {
+    pub(crate) const fn ascii_change_case_unchecked(&self) -> u8 {
         *self ^ ASCII_CASE_MASK
     }