diff --git a/src/lib/maybe_owned_slice.rs b/src/lib/maybe_owned_slice.rs
index 18fecab9d..aff79e3d1 100644
--- a/src/lib/maybe_owned_slice.rs
+++ b/src/lib/maybe_owned_slice.rs
@@ -61,8 +61,6 @@ impl<'a, T : 'a> Index<usize> for MaybeOwnedSlice<'a, T> {
 }
 
 impl<'a, T : 'a> IndexMut<usize> for MaybeOwnedSlice<'a, T> {
-    type Output = T;
-
     #[inline]
     fn index_mut<'b>(&'b mut self, index: &usize) -> &'b mut T {
         &mut self.as_mut_slice()[*index]
diff --git a/src/lib/repeated.rs b/src/lib/repeated.rs
index 86e5a1f94..7bee2be98 100644
--- a/src/lib/repeated.rs
+++ b/src/lib/repeated.rs
@@ -296,8 +296,6 @@ impl<T> Index<usize> for RepeatedField<T> {
 }
 
 impl<T> IndexMut<usize> for RepeatedField<T> {
-    type Output = T;
-
     #[inline]
     fn index_mut<'a>(&'a mut self, index: &usize) -> &'a mut T {
         &mut self.as_mut_slice()[*index]