diff --git a/response_schema.json b/response_schema.json
index 09f71ae..88814b1 100644
--- a/response_schema.json
+++ b/response_schema.json
@@ -15,7 +15,7 @@
       "description": "HD Model Grade"
     },
     "reason_description": {
-      "type": "string",
+      "type": ["string", "null"],
       "description": "Reason for the model decision"
     }
   }