1 files changed, 1 insertions, 1 deletions
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 49f8aa25ea..a9364670a1 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -1401,7 +1401,7 @@ class EventCreationHandler:
         ]
 
         for k in immutable_fields:
-            if getattr(builder, k, None) != original_event.get(k):
+            if getattr(builder, k, None) != getattr(original_event, k, None):
                 raise Exception(
                     "Third party rules module created an invalid event: "
                     "cannot change field " + k