diff --git a/Python/ceval.c b/Python/ceval.c
index 718bb32..b3ec013 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -3107,6 +3107,8 @@
         tail = PyUnicode_FromFormat(", %U, and %U",
                                     PyList_GET_ITEM(names, len - 2),
                                     PyList_GET_ITEM(names, len - 1));
+        if (tail == NULL)
+            return;
         /* Chop off the last two objects in the list. This shouldn't actually
            fail, but we can't be too careful. */
         err = PyList_SetSlice(names, len - 2, len, NULL);