diff --git a/http-body-util/src/combinators/map_frame.rs b/http-body-util/src/combinators/map_frame.rs
index 44886bd..7323b5d 100644
--- a/http-body-util/src/combinators/map_frame.rs
+++ b/http-body-util/src/combinators/map_frame.rs
@@ -72,6 +72,10 @@ where
     fn is_end_stream(&self) -> bool {
         self.inner.is_end_stream()
     }
+
+    fn size_hint(&self) -> http_body::SizeHint {
+        self.inner.size_hint()
+    }
 }
 
 impl<B, F> fmt::Debug for MapFrame<B, F>