diff --git a/backend/open_webui/utils/oauth.py b/backend/open_webui/utils/oauth.py
index aa5bc47df6..1a4ed3871c 100644
--- a/backend/open_webui/utils/oauth.py
+++ b/backend/open_webui/utils/oauth.py
@@ -1081,21 +1081,30 @@ class OAuthManager:
             log.debug(f'Accepted user roles: {oauth_allowed_roles}')
             log.debug(f'Accepted admin roles: {oauth_admin_roles}')
 
-            # If any roles are found, check if they match the allowed or admin roles
+            # If roles are present in the token, they must match; otherwise deny access
             if oauth_roles:
-                # If role management is enabled, and matching roles are provided, use the roles
+                matched = False
                 for allowed_role in oauth_allowed_roles:
-                    # If the user has any of the allowed roles, assign the role "user"
                     if allowed_role in oauth_roles:
                         log.debug('Assigned user the user role')
                         role = 'user'
+                        matched = True
                         break
                 for admin_role in oauth_admin_roles:
-                    # If the user has any of the admin roles, assign the role "admin"
                     if admin_role in oauth_roles:
                         log.debug('Assigned user the admin role')
                         role = 'admin'
+                        matched = True
                         break
+                if not matched:
+                    log.warning(
+                        f'OAuth role management enabled but user roles do not match any allowed/admin roles. '
+                        f'User roles: {oauth_roles}, allowed: {oauth_allowed_roles}, admin: {oauth_admin_roles}'
+                    )
+                    raise HTTPException(
+                        status.HTTP_403_FORBIDDEN,
+                        detail=ERROR_MESSAGES.ACCESS_PROHIBITED,
+                    )
         else:
             if not user:
                 # If role management is disabled, use the default role for new users