diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index cc4612f9308..4582dfb6afe 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -4083,6 +4083,16 @@ _PyStaticType_Dealloc(PyTypeObject *type)
     // A subtype can inherit attributes and methods of its parent type,
     // and a type must no longer be used once it's deallocated.
     if (type->tp_subclasses != NULL) {
+        if (type->tp_subclasses != NULL) {
+            fprintf(stderr, "Cannot deallocate type '%s': it still has subclasses\n", type->tp_name);
+            Py_ssize_t i = 0;
+            PyObject *ref;
+            while (PyDict_Next(type->tp_subclasses, &i, NULL, &ref)) {
+                PyObject *obj = PyWeakref_GET_OBJECT(ref);
+                PyTypeObject *subclass = _PyType_CAST(obj);
+                fprintf(stderr, "* %s\n", subclass->tp_name);
+            }
+        }
         return;
     }