diff --git a/testing/mochitest/tests/index.html b/testing/mochitest/tests/index.html
index 05717f3ba7f8..dc6850e9dd4a 100644
--- a/testing/mochitest/tests/index.html
+++ b/testing/mochitest/tests/index.html
@@ -30,7 +30,7 @@ if (params.closeWhenDone) {
 // logFile to write our results
 if (params.logFile) {
   MozillaFileLogger.init(params.logFile);
-  TestRunner.logger.addListener("mozLogger", fileLevel, MozillaFileLogger.getLogCallback());
+  TestRunner.logger.addListener("mozLogger", fileLevel + "", MozillaFileLogger.getLogCallback());
 }
 
 // if we get a quiet param, don't log to the console