diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2286,6 +2286,7 @@
         __alloc_traits::deallocate(__alloc(), __old_p, __old_cap + 1);
     __set_long_pointer(__p);
     __set_long_cap(__allocation.count);
+    __set_long_size(__old_sz);
 }
 
 // assign