diff --git a/synapse/storage/transactions.py b/synapse/storage/transactions.py
index 4c3dc5866..7e3add528 100644
--- a/synapse/storage/transactions.py
+++ b/synapse/storage/transactions.py
@@ -184,7 +184,7 @@ class TransactionStore(SQLBaseStore):
             },
             updatevalues={
                 "response_code": code,
-                "response_json": response_json,
+                "response_json": None,  # For now, don't persist response_json
             }
         )