diff --git a/tracker/rabit_hadoop.py b/tracker/rabit_hadoop.py
index 5c9f06948..089e50335 100755
--- a/tracker/rabit_hadoop.py
+++ b/tracker/rabit_hadoop.py
@@ -36,7 +36,7 @@ if hadoop_streaming_jar != None:
 
 def hadoop_streaming(nslaves, slave_args):
   cmd = '%s jar %s' % (args.hadoop_binary, args.hadoop_streaming_jar)
-  cmd += ' -input %s -output %s'  (args.input, args.output)
+  cmd += ' -input %s -output %s' % (args.input, args.output)
   cmd += ' -mapper \"%s %s %s\" -reducer \"/bin/cat\" ' % (args.mapper, args.args, ' '.join(slave_args))
   cmd += ' -file %s -D mapred.map.tasks=%d' % (args.mapper, nslaves)
   print cmd