diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 974a4029e06..cda517024a6 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -2898,7 +2898,7 @@ same_slots_added(PyTypeObject *a, PyTypeObject *b)
     PyObject *slots_a, *slots_b;
 
     assert(base == b->tp_base);
-    assert(equiv_structs(a, base) && equiv_structs(b, base));
+    assert(!equiv_structs(a, base) && !equiv_structs(b, base));
     size = base->tp_basicsize;
     if (a->tp_dictoffset == size && b->tp_dictoffset == size)
         size += sizeof(PyObject *);