diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index db923c164774b7..58f1320c1c9ec0 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -1747,7 +1747,7 @@ static int recurse_down_subclasses(PyTypeObject *type, PyObject *name,
 // Compute tp_mro for this type and all of its subclasses.  This
 // is called after __bases__ is assigned to an existing type.
 static int
-mro_hierarchy(PyTypeObject *type, PyObject *temp)
+mro_hierarchy_for_complete_type(PyTypeObject *type, PyObject *temp)
 {
     ASSERT_TYPE_LOCK_HELD();
 
@@ -1758,6 +1758,7 @@ mro_hierarchy(PyTypeObject *type, PyObject *temp)
         return res;
     }
     PyObject *new_mro = lookup_tp_mro(type);
+    assert(new_mro != NULL);
 
     PyObject *tuple;
     if (old_mro != NULL) {
@@ -1802,7 +1803,7 @@ mro_hierarchy(PyTypeObject *type, PyObject *temp)
         Py_ssize_t n = PyList_GET_SIZE(subclasses);
         for (Py_ssize_t i = 0; i < n; i++) {
             PyTypeObject *subclass = _PyType_CAST(PyList_GET_ITEM(subclasses, i));
-            res = mro_hierarchy(subclass, temp);
+            res = mro_hierarchy_for_complete_type(subclass, temp);
             if (res < 0) {
                 break;
             }
@@ -1893,7 +1894,7 @@ type_set_bases_unlocked(PyTypeObject *type, PyObject *new_bases, PyTypeObject *b
     if (temp == NULL) {
         goto bail;
     }
-    if (mro_hierarchy(type, temp) < 0) {
+    if (mro_hierarchy_for_complete_type(type, temp) < 0) {
         goto undo;
     }
     Py_DECREF(temp);
@@ -3398,6 +3399,7 @@ mro_implementation_unlocked(PyTypeObject *type)
          */
         PyTypeObject *base = _PyType_CAST(PyTuple_GET_ITEM(bases, 0));
         PyObject *base_mro = lookup_tp_mro(base);
+        assert(base_mro != NULL);
         Py_ssize_t k = PyTuple_GET_SIZE(base_mro);
         PyObject *result = PyTuple_New(k + 1);
         if (result == NULL) {
@@ -3432,9 +3434,12 @@ mro_implementation_unlocked(PyTypeObject *type)
         return NULL;
     }
 
+    PyObject *mro_to_merge;
     for (Py_ssize_t i = 0; i < n; i++) {
         PyTypeObject *base = _PyType_CAST(PyTuple_GET_ITEM(bases, i));
-        to_merge[i] = lookup_tp_mro(base);
+        mro_to_merge = lookup_tp_mro(base);
+        assert(mro_to_merge != NULL);
+        to_merge[i] = mro_to_merge;
     }
     to_merge[n] = bases;
 
@@ -8913,6 +8918,7 @@ type_ready_inherit(PyTypeObject *type)
 
     // Inherit slots
     PyObject *mro = lookup_tp_mro(type);
+    assert(mro != NULL);
     Py_ssize_t n = PyTuple_GET_SIZE(mro);
     for (Py_ssize_t i = 1; i < n; i++) {
         PyObject *b = PyTuple_GET_ITEM(mro, i);