diff --git a/src/controllers/PermissionController.ts b/src/controllers/PermissionController.ts
index e123e81..663343c 100644
--- a/src/controllers/PermissionController.ts
+++ b/src/controllers/PermissionController.ts
@@ -90,7 +90,7 @@ export class PermissionController {
         if (oldPermission.id != permission.id) {
             throw new PermissionIdsNotMatchingError();
         }
-        let existingPermission = await this.permissionRepository.findOne({ target: permission.target, action: permission.action, principal: permission.principal }, { relations: ['principal'] });
+        let existingPermission = await this.permissionRepository.findOne({ target: permission.target, action: permission.action, principal: await permission.getPrincipal() }, { relations: ['principal'] });
         if (existingPermission) {
             await this.remove(permission.id, true);
             return new ResponsePermission(existingPermission);