diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
index e78399ddefa..b6cceee27f5 100644
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -2277,7 +2277,9 @@ _count_elements(PyObject *self, PyObject *args)
     dict_setitem = _PyType_LookupId(&PyDict_Type, &PyId___setitem__);
 
     if (mapping_get != NULL && mapping_get == dict_get &&
-        mapping_setitem != NULL && mapping_setitem == dict_setitem) {
+        mapping_setitem != NULL && mapping_setitem == dict_setitem &&
+        PyDict_Check(mapping))
+    {
         while (1) {
             /* Fast path advantages:
                    1. Eliminate double hashing