diff --git a/packages/model3d-viewer/src/loader.ts b/packages/model3d-viewer/src/loader.ts
index f28303b8d..6c6caac40 100644
--- a/packages/model3d-viewer/src/loader.ts
+++ b/packages/model3d-viewer/src/loader.ts
@@ -404,7 +404,15 @@ export async function loadModel3dViewerObject(
       format === 'gltf' ? new TextDecoder().decode(new Uint8Array(data)) : data;
     const gltf = await new Promise<{ scene: ThreeTypes.Object3D }>(
       (resolve, reject) => {
-        loader.parse(payload, basePath, resolve, reject);
+        loader.parse(payload, basePath, resolve, (error) => {
+          // GLTFLoader 的 onError 回传的是 ErrorEvent（不是 Error）：直接 reject，
+          // 外层 describeModel3dViewerError 只会拿到「未知错误」，真实解析原因被丢掉。
+          const detail =
+            typeof error === 'object' && error !== null && 'message' in error
+              ? String((error as { message?: unknown }).message ?? '')
+              : '';
+          reject(new Error(detail.trim() || describeModel3dViewerError(error)));
+        });
       },
     );
     return gltf.scene;