diff --git a/objectifier-module.nix b/objectifier-module.nix
index 5df95ca..d22476d 100644
--- a/objectifier-module.nix
+++ b/objectifier-module.nix
@@ -75,7 +75,8 @@ in {
         PIDFile = "/run/objectifier.pid";
         ExecStart = let
           bindClause = concatStringsSep " "
-            (map (addr: "--bind ${addr}:${cfg.port}") cfg.listen-addresses);
+            (map (addr: "--bind ${addr}:${toString cfg.port}")
+              cfg.listen-addresses);
         in (concatStringsSep " " [
           "gunicorn"
           bindClause