diff --git a/lib/queue.js b/lib/queue.js
index 522107a5f..6af6e121c 100755
--- a/lib/queue.js
+++ b/lib/queue.js
@@ -629,7 +629,7 @@ Queue.prototype.setHandler = function(name, handler) {
     const supportedFileTypes = ['js', 'ts', 'flow'];
     const processorFile =
       handler +
-      (supportedFileTypes.indexOf(path.extname(handler)) !== '-1' ? '' : '.js');
+      (supportedFileTypes.indexOf(path.extname(handler)) !== -1 ? '' : '.js');
 
     if (!fs.existsSync(processorFile)) {
       throw new Error('File ' + processorFile + ' does not exist');