diff --git a/mail-server/dovecot.nix b/mail-server/dovecot.nix
index ff2b3e6..c75aff2 100644
--- a/mail-server/dovecot.nix
+++ b/mail-server/dovecot.nix
@@ -125,9 +125,7 @@ let
     cat <<EOF > ${userdbFile}
     ${lib.concatStringsSep "\n" (lib.mapAttrsToList (name: value:
       "${name}:::::::"
-        + (if lib.isString value.quota
-              then "userdb_quota_rule=*:storage=${value.quota}"
-              else "")
+        + lib.optionalString (value.quota != null) "userdb_quota_rule=*:storage=${value.quota}"
     ) cfg.loginAccounts)}
     EOF
   '';