diff --git a/swh/objstorage/api/server.py b/swh/objstorage/api/server.py
index 720ecee4693c494e3e60ab60ab6b65f9430186d4..a35959504a69719e8c43a406c44260ba322e3068 100644
--- a/swh/objstorage/api/server.py
+++ b/swh/objstorage/api/server.py
@@ -86,8 +86,13 @@ app = ObjStorageServerApp(
 objstorage = None
 
 
-@app.errorhandler(Error)
+@app.errorhandler(ObjNotFoundError)
 def argument_error_handler(exception):
+    return error_handler(exception, encode_data, status_code=404)
+
+
+@app.errorhandler(Error)
+def objnotfound_error_handler(exception):
     return error_handler(exception, encode_data, status_code=400)