diff --git a/test/core/utils/memoize.js b/test/core/utils/memoize.js
index 7c85033614..ec3e3baee5 100644
--- a/test/core/utils/memoize.js
+++ b/test/core/utils/memoize.js
@@ -2,9 +2,9 @@ describe('axe.utils.memoize', function () {
   'use strict';
 
   it('should add the function to axe._memoizedFns', function () {
-    axe._memoizedFns.length = 0;
+    const length = axe._memoizedFns.length;
 
     axe.utils.memoize(function myFn() {});
-    assert.equal(axe._memoizedFns.length, 1);
+    assert.equal(axe._memoizedFns.length, length + 1);
   });
 });