diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -2266,7 +2266,11 @@
     if (this != &__str)
     {
         __copy_assign_alloc(__str);
-        return assign(__str.data(), __str.size());
+        const bool __str_is_long = __str.__is_long();
+        if (__str_is_long || __is_long()) {
+          return assign(__str.data(), __str.size());
+        }
+        __r_.first().__r = __str.__r_.first().__r;
     }
     return *this;
 }