3 files changed, 12 insertions, 6 deletions
diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index 4252e5ab5c..bf07951027 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -18,7 +18,7 @@ from synapse.util.frozenutils import freeze, unfreeze
 
 class _EventInternalMetadata(object):
     def __init__(self, internal_metadata_dict):
-        self.__dict__ = internal_metadata_dict
+        self.__dict__ = dict(internal_metadata_dict)
 
     def get_dict(self):
         return dict(self.__dict__)
diff --git a/synapse/events/builder.py b/synapse/events/builder.py
index a9b1b99a10..9d45bdb892 100644
--- a/synapse/events/builder.py
+++ b/synapse/events/builder.py
@@ -23,14 +23,15 @@ import copy
 
 
 class EventBuilder(EventBase):
-    def __init__(self, key_values={}):
+    def __init__(self, key_values={}, internal_metadata_dict={}):
         signatures = copy.deepcopy(key_values.pop("signatures", {}))
         unsigned = copy.deepcopy(key_values.pop("unsigned", {}))
 
         super(EventBuilder, self).__init__(
             key_values,
             signatures=signatures,
-            unsigned=unsigned
+            unsigned=unsigned,
+            internal_metadata_dict=internal_metadata_dict,
         )
 
     def build(self):
diff --git a/synapse/events/utils.py b/synapse/events/utils.py
index 21316cc125..1aa952150e 100644
--- a/synapse/events/utils.py
+++ b/synapse/events/utils.py
@@ -45,12 +45,14 @@ def prune_event(event):
         "membership",
     ]
 
+    event_dict = event.get_dict()
+
     new_content = {}
 
     def add_fields(*fields):
         for field in fields:
             if field in event.content:
-                new_content[field] = event.content[field]
+                new_content[field] = event_dict["content"][field]
 
     if event_type == EventTypes.Member:
         add_fields("membership")
@@ -75,7 +77,7 @@ def prune_event(event):
 
     allowed_fields = {
         k: v
-        for k, v in event.get_dict().items()
+        for k, v in event_dict.items()
         if k in allowed_keys
     }
 
@@ -86,7 +88,10 @@ def prune_event(event):
     if "age_ts" in event.unsigned:
         allowed_fields["unsigned"]["age_ts"] = event.unsigned["age_ts"]
 
-    return type(event)(allowed_fields)
+    return type(event)(
+        allowed_fields,
+        internal_metadata_dict=event.internal_metadata.get_dict()
+    )
 
 
 def format_event_raw(d):