diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index 21060182d60..c9c8f68cd9c 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -826,7 +826,7 @@ pub fn is_ascii(&self) -> bool {
     /// assert!(!OsString::from("Ferrös").eq_ignore_ascii_case("FERRÖS"));
     /// ```
     #[unstable(feature = "osstring_ascii", issue = "70516")]
-    pub fn eq_ignore_ascii_case<S: ?Sized + AsRef<OsStr>>(&self, other: &S) -> bool {
+    pub fn eq_ignore_ascii_case<S: AsRef<OsStr>>(&self, other: S) -> bool {
         self.inner.eq_ignore_ascii_case(&other.as_ref().inner)
     }
 }