diff --git a/apps/api/src/auth/role-weight.ts b/apps/api/src/auth/role-weight.ts
index 90ff841..839312c 100644
--- a/apps/api/src/auth/role-weight.ts
+++ b/apps/api/src/auth/role-weight.ts
@@ -1,4 +1,4 @@
-import { ForbiddenException } from "@nestjs/common";
+import { BadRequestException, ForbiddenException } from "@nestjs/common";
 import { rolesRepo } from "@eden/database";
 import { SUPER_ADMIN_ROLE } from "./permissions.js";
 
@@ -7,20 +7,23 @@ import { SUPER_ADMIN_ROLE } from "./permissions.js";
  * heavier than their own, nor act on a user whose *current* role is
  * heavier than the actor's — orthogonal to the resource/action/scope
  * permission check. super_admin (weight 100, hardcoded ceiling) always
- * passes both checks.
+ * passes the *weight comparison* — but role existence is still validated
+ * even for super_admin, otherwise an invalid role key would sail past
+ * this check and only fail later as an unhandled FK-constraint 500 from
+ * the database (an earlier bug caught by manual testing: this function
+ * must be the single place that turns "role doesn't exist" into a clean
+ * 400, not the DB constraint).
  */
 async function getWeight(roleKey: string): Promise<number> {
   const role = await rolesRepo.getRoleByKey(roleKey);
-  if (!role) throw new ForbiddenException("Papel inválido");
+  if (!role) throw new BadRequestException(`Papel '${roleKey}' não existe`);
   return role.weight;
 }
 
 export async function assertCanAssignRole(actorRoleKey: string, targetRoleKey: string): Promise<void> {
+  const targetWeight = await getWeight(targetRoleKey);
   if (actorRoleKey === SUPER_ADMIN_ROLE) return;
-  const [actorWeight, targetWeight] = await Promise.all([
-    getWeight(actorRoleKey),
-    getWeight(targetRoleKey),
-  ]);
+  const actorWeight = await getWeight(actorRoleKey);
   if (targetWeight > actorWeight) {
     throw new ForbiddenException("Você não pode atribuir um papel com peso maior que o seu.");
   }
@@ -30,11 +33,9 @@ export async function assertCanActOnUser(
   actorRoleKey: string,
   targetUserRoleKey: string,
 ): Promise<void> {
+  const targetWeight = await getWeight(targetUserRoleKey);
   if (actorRoleKey === SUPER_ADMIN_ROLE) return;
-  const [actorWeight, targetWeight] = await Promise.all([
-    getWeight(actorRoleKey),
-    getWeight(targetUserRoleKey),
-  ]);
+  const actorWeight = await getWeight(actorRoleKey);
   if (targetWeight > actorWeight) {
     throw new ForbiddenException("Você não pode alterar um usuário com papel de peso maior que o seu.");
   }