diff --git a/labeler/adapter/fastapi_srv.py b/labeler/adapter/fastapi_srv.py
index 6b0cf75..1aaf482 100644
--- a/labeler/adapter/fastapi_srv.py
+++ b/labeler/adapter/fastapi_srv.py
@@ -73,7 +73,7 @@ class LabelingBot:
 
 @app.get("/", response_class=HTMLResponse)
 async def root():
-    with open("fegen/docs/index.html", "r") as f:
+    with open("fegen/docs/index.html", "rb") as f:
         index = f.read()
     return index