diff --git a/server/build_image.py b/server/build_image.py
index 59cc630..e07e1c6 100755
--- a/server/build_image.py
+++ b/server/build_image.py
@@ -28,7 +28,7 @@ parser.add_argument(
 parser.add_argument(
     '--module',
     dest='modules',
-    nargs='*')
+    action='append')
 parser.add_argument(
     '--release',
     dest='release',