diff --git a/challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming.json b/challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming.json
index 1b48605dce..2177997691 100644
--- a/challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming.json
+++ b/challenges/02-javascript-algorithms-and-data-structures/object-oriented-programming.json
@@ -393,7 +393,8 @@
       ],
       "tests": [
         "assert(ownProps.includes('name'), 'message: The <code>ownProps</code> array should include <code>\"name\"</code>.');",
-        "assert(prototypeProps.includes('numLegs'), 'message: The <code>prototypeProps</code> array should include <code>\"numLegs\"</code>.');"
+        "assert(prototypeProps.includes('numLegs'), 'message: The <code>prototypeProps</code> array should include <code>\"numLegs\"</code>.');",
+        "assert(!/\\Object.keys/.test(code), 'message: Solve this challenge without using the built in method <code>Object.keys()</code>.');"
       ],
       "solutions": [],
       "hints": [],