diff --git a/machines/modules/docker-stack.nix b/machines/modules/docker-stack.nix
index 18017ab..fbb8546 100644
--- a/machines/modules/docker-stack.nix
+++ b/machines/modules/docker-stack.nix
@@ -97,7 +97,7 @@ let
       };
 
       deploy = {
-        labels = {
+        labels = mkOption {
           default = [ ];
           type = types.listOf types.str;
           description = lib.mdDoc "Specify labels for the service.";