diff --git a/library/std/src/sync/nonpoison/mutex.rs b/library/std/src/sync/nonpoison/mutex.rs
index ed3f8cfed821a..307bf8eaf512e 100644
--- a/library/std/src/sync/nonpoison/mutex.rs
+++ b/library/std/src/sync/nonpoison/mutex.rs
@@ -422,7 +422,7 @@ impl<T> From<T> for Mutex<T> {
 }
 
 #[unstable(feature = "nonpoison_mutex", issue = "134645")]
-impl<T: ?Sized + Default> Default for Mutex<T> {
+impl<T: Default> Default for Mutex<T> {
     /// Creates a `Mutex<T>`, with the `Default` value for T.
     fn default() -> Mutex<T> {
         Mutex::new(Default::default())
diff --git a/library/std/src/sync/poison/mutex.rs b/library/std/src/sync/poison/mutex.rs
index 7f9e5fe62516f..6eccd8a875edd 100644
--- a/library/std/src/sync/poison/mutex.rs
+++ b/library/std/src/sync/poison/mutex.rs
@@ -688,7 +688,7 @@ impl<T> From<T> for Mutex<T> {
 }
 
 #[stable(feature = "mutex_default", since = "1.10.0")]
-impl<T: ?Sized + Default> Default for Mutex<T> {
+impl<T: Default> Default for Mutex<T> {
     /// Creates a `Mutex<T>`, with the `Default` value for T.
     fn default() -> Mutex<T> {
         Mutex::new(Default::default())