diff --git a/library/core/src/error.rs b/library/core/src/error.rs
index 150e4f3f318..ca8983d4cbc 100644
--- a/library/core/src/error.rs
+++ b/library/core/src/error.rs
@@ -1008,8 +1008,15 @@ fn next(&mut self) -> Option<Self::Item> {
         self.current = self.current.and_then(Error::source);
         current
     }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        if self.current.is_some() { (1, None) } else { (0, Some(0)) }
+    }
 }
 
+#[unstable(feature = "error_iter", issue = "58520")]
+impl<'a> crate::iter::FusedIterator for Source<'a> {}
+
 #[stable(feature = "error_by_ref", since = "1.51.0")]
 impl<'a, T: Error + ?Sized> Error for &'a T {
     #[allow(deprecated, deprecated_in_future)]