diff --git a/tempest/cmd/run.py b/tempest/cmd/run.py
index 3e84b82..a8ef08c 100644
--- a/tempest/cmd/run.py
+++ b/tempest/cmd/run.py
@@ -252,6 +252,7 @@
                             default=False)
         # execution args
         parser.add_argument('--concurrency', '-w',
+                            type=int,
                             help="The number of workers to use, defaults to "
                                  "the number of cpus")
         parallel = parser.add_mutually_exclusive_group()