diff --git a/schemas/api/trains/TrainDetails.json b/schemas/api/trains/TrainDetails.json
index 000bbf1..b0b4fa7 100644
--- a/schemas/api/trains/TrainDetails.json
+++ b/schemas/api/trains/TrainDetails.json
@@ -218,7 +218,7 @@
             }
         },
         "pis": {
-            "$ref": "./schemas/api/pis-object.json"
+            "description": "PIS data for the service (if available)"
         }
     }
 }
\ No newline at end of file