diff --git a/nixos/modules/services/web-apps/keycloak.nix b/nixos/modules/services/web-apps/keycloak.nix
index 8986e9fb0abe..38ade3560dee 100644
--- a/nixos/modules/services/web-apps/keycloak.nix
+++ b/nixos/modules/services/web-apps/keycloak.nix
@@ -54,6 +54,7 @@ in
 
     frontendUrl = lib.mkOption {
       type = lib.types.str;
+      apply = x: if lib.hasSuffix "/" x then x else x + "/";
       example = "keycloak.example.com/auth";
       description = ''
         The public URL used as base for all frontend requests. Should