diff --git a/include/algorithm b/include/algorithm
index 0f6107b..e24f979 100644
--- a/include/algorithm
+++ b/include/algorithm
@@ -1528,10 +1528,10 @@
 
 // copy_backward
 
-template <class _InputIterator, class _OutputIterator>
+template <class _BidirectionalIterator, class _OutputIterator>
 inline _LIBCPP_INLINE_VISIBILITY
 _OutputIterator
-__copy_backward(_InputIterator __first, _InputIterator __last, _OutputIterator __result)
+__copy_backward(_BidirectionalIterator __first, _BidirectionalIterator __last, _OutputIterator __result)
 {
     while (__first != __last)
         *--__result = *--__last;