diff --git a/backend/src/app/core/auth.py b/backend/src/app/core/auth.py
index 84cffaf..8c28b5d 100644
--- a/backend/src/app/core/auth.py
+++ b/backend/src/app/core/auth.py
@@ -26,11 +26,21 @@ class AuthUser:
     role: str | None = None
 
 
+def _build_jwks_url(base_url: str) -> str:
+    """Build the JWKS URL, adding /auth/v1 prefix for Supabase Cloud."""
+    base = base_url.rstrip("/")
+    if "/auth/v1" in base:
+        return f"{base}/.well-known/jwks.json"
+    # Supabase Cloud URLs need the /auth/v1 prefix;
+    # local GoTrue serves JWKS at root but uses HS256 fallback anyway.
+    return f"{base}/auth/v1/.well-known/jwks.json"
+
+
 def _get_jwks_client() -> PyJWKClient | None:
     """Get or create a cached JWKS client."""
     global _jwks_client
     if _jwks_client is None and settings.supabase_url:
-        jwks_url = f"{settings.supabase_url.rstrip('/')}/.well-known/jwks.json"
+        jwks_url = _build_jwks_url(settings.supabase_url)
         _jwks_client = PyJWKClient(jwks_url, cache_jwk_set=True, lifespan=300)
     return _jwks_client