diff --git a/discover_jenkins/tasks/run_jshint.py b/discover_jenkins/tasks/run_jshint.py
index a76d987..b969c5c 100644
--- a/discover_jenkins/tasks/run_jshint.py
+++ b/discover_jenkins/tasks/run_jshint.py
@@ -82,7 +82,7 @@ class Task(object):
         output, err = process.communicate()
         retcode = process.poll()
         if retcode not in [0, 2]:  # normal jshint return codes
-            raise CalledProcessError(retcode, cmd, output=output + '\n' + err)
+            raise CalledProcessError(retcode, cmd, output='%s\n%s' % (output, err))
 
         self.output.write(output.decode('utf-8'))