diff --git a/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst b/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst
new file mode 100644
index 00000000000000..f78f1b2b1a5a14
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-10-15-06-28-50.bpo-42034.MonocleAI.rst
@@ -0,0 +1 @@
+Fix unchecked return in Objects/typeobject.c. The return value of a function that is potentially used to initialize a local variable is not checked. Therefore, reading the local variable may result in undefined behavior.
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 3bb2c338fe0b53..dab57147cf2895 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -823,14 +823,15 @@ type_set_bases(PyTypeObject *type, PyObject *new_bases, void *context)
         PyTypeObject *cls;
         PyObject *new_mro, *old_mro = NULL;
 
-        PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
-                          "", 2, 3, &cls, &new_mro, &old_mro);
-        /* Do not rollback if cls has a newer version of MRO.  */
-        if (cls->tp_mro == new_mro) {
-            Py_XINCREF(old_mro);
-            cls->tp_mro = old_mro;
-            Py_DECREF(new_mro);
-        }
+        if(PyArg_UnpackTuple(PyList_GET_ITEM(temp, i),
+                          "", 2, 3, &cls, &new_mro, &old_mro)) {
+           /* Do not rollback if cls has a newer version of MRO.  */
+           if (cls->tp_mro == new_mro) {
+               Py_XINCREF(old_mro);
+               cls->tp_mro = old_mro;
+               Py_DECREF(new_mro);
+           }
+        } 
     }
     Py_DECREF(temp);