diff --git a/esquery.js b/esquery.js
index d4d9fea..1006262 100644
--- a/esquery.js
+++ b/esquery.js
@@ -226,6 +226,7 @@
             var parent = ancestry[0], listProp, keys, i, l, idx;
             if (!parent) { return false; }
             keys = estraverse.VisitorKeys[parent.type];
+            if (!keys) { return false; }
             for (i = 0, l = keys.length; i < l; ++i) {
                 listProp = parent[keys[i]];
                 if (isArray(listProp)) {