diff --git a/library/std/src/io/mod.rs b/library/std/src/io/mod.rs
index 018fe1c52bfb..e9c99e5a6273 100644
--- a/library/std/src/io/mod.rs
+++ b/library/std/src/io/mod.rs
@@ -2481,7 +2481,7 @@ impl<R: Read + SizeHint> Iterator for Bytes<R> {
 
 #[stable(feature = "bufreader_size_hint", since = "1.51.0")]
 trait SizeHint {
-    fn lower_bound(&self) -> usize {
+    fn lower_bound(&self) -> usize;
 
     fn upper_bound(&self) -> Option<usize> {
         None