diff --git a/shells/dodona.nix b/shells/dodona.nix
index c4e0ade6..2a36deb4 100644
--- a/shells/dodona.nix
+++ b/shells/dodona.nix
@@ -9,7 +9,7 @@ let
   '';
   support-procfile = pkgs.writeText "Procfile.supp" support-procfile-text;
   all-procfile-text = support-procfile-text + ''
-    server: rails s
+    server: rails s -p 3000
   '';
   all-procfile = pkgs.writeText "Procfile.all" all-procfile-text;