diff --git a/Python/hamt.c b/Python/hamt.c
index 8998dbd..c9acbbc 100644
--- a/Python/hamt.c
+++ b/Python/hamt.c
@@ -2358,6 +2358,8 @@
             Py_INCREF(o);
             return o;
         case W_NEWNODE: {
+            assert(new_root != NULL);
+
             PyHamtObject *new_o = hamt_alloc();
             if (new_o == NULL) {
                 Py_DECREF(new_root);