diff --git a/packages/overlayscrollbars/tests/jest/support/dom/class.test.ts b/packages/overlayscrollbars/tests/jest/support/dom/class.test.ts
index 450a14d..a2af6bc 100644
--- a/packages/overlayscrollbars/tests/jest/support/dom/class.test.ts
+++ b/packages/overlayscrollbars/tests/jest/support/dom/class.test.ts
@@ -45,7 +45,7 @@ describe('dom class names', () => {
     });
 
     test('null', () => {
-      expect(addClass(null, 'abc')).toBe(undefined);
+      expect(typeof addClass(null, 'abc')).toBe('function');
     });
   });