diff --git a/addons/jest/src/index.js b/addons/jest/src/index.js
index e302a7a0f077..b68a1e0b83fd 100644
--- a/addons/jest/src/index.js
+++ b/addons/jest/src/index.js
@@ -1,6 +1,6 @@
 import addons from '@storybook/addons';
 
-const findTestResults = (testFiles, jestTestResults, jestTestFilesExt) =>
+const findTestResults = (testFiles, jestTestResults, jestTestFilesExt = "") =>
   testFiles.map(name => {
     if (jestTestResults && jestTestResults.testResults) {
       return {