diff --git a/synapse/api/events/utils.py b/synapse/api/events/utils.py
index dfefb2662a..3d8b9a1db1 100644
--- a/synapse/api/events/utils.py
+++ b/synapse/api/events/utils.py
@@ -13,7 +13,11 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from .room import RoomMemberEvent
+from .room import (
+    RoomMemberEvent, RoomJoinRulesEvent, RoomPowerLevelsEvent,
+    RoomAddStateLevelEvent, RoomSendEventLevelEvent, RoomOpsPowerLevelsEvent,
+    RoomAliasesEvent, RoomCreateEvent,
+)
 
 def prune_event(event):
     """ Prunes the given event of all keys we don't know about or think could
@@ -27,12 +31,33 @@ def prune_event(event):
     # Remove all extraneous fields.
     event.unrecognized_keys = {}
 
+    new_content = {}
+
+    def add_fields(*fields):
+        for field in fields:
+            if field in event.content:
+                new_content[field] = event.content[field]
+
     if event.type == RoomMemberEvent.TYPE:
-        new_content = {
-            "membership": event.content["membership"]
-        }
-    else:
-        new_content = {}
+        add_fields("membership")
+    elif event.type == RoomCreateEvent.TYPE:
+        add_fields("creator")
+    elif event.type == RoomJoinRulesEvent.TYPE:
+        add_fields("join_rule")
+    elif event.type == RoomPowerLevelsEvent.TYPE:
+        # TODO: Actually check these are valid user_ids etc.
+        add_fields("default")
+        for k, v in event.content.items():
+            if k.startswith("@") and isinstance(v, (int, long)):
+                new_content[k] = v
+    elif event.type == RoomAddStateLevelEvent.TYPE:
+        add_fields("level")
+    elif event.type == RoomSendEventLevelEvent.TYPE:
+        add_fields("level")
+    elif event.type == RoomOpsPowerLevelsEvent.TYPE:
+        add_fields("kick_level", "ban_level", "delete_level")
+    elif event.type == RoomAliasesEvent.TYPE:
+        add_fields("aliases")
 
     event.content = new_content