diff --git a/lib/karma-parallelizer.js b/lib/karma-parallelizer.js
index dda9075..3578f16 100644
--- a/lib/karma-parallelizer.js
+++ b/lib/karma-parallelizer.js
@@ -5,7 +5,7 @@
 function initKarmaParallelizer(root, karma, shardIndexInfoMap) {
   var idParamExtractor = /(\?|&)id=(\d+)(&|$)/;
   const parentWindow = window.opener || window.parent;
-  var matches = idParamExtractor.exec(parentWindow.location.search);
+  var matches = idParamExtractor.exec(parentWindow.location.search || opener.location.search);
   var id = (matches && matches[2]) || null;
 
   if (