diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py
index e673e96cc..c3ff85c49 100644
--- a/synapse/events/__init__.py
+++ b/synapse/events/__init__.py
@@ -47,14 +47,26 @@ class _EventInternalMetadata(object):
 
 
 def _event_dict_property(key):
+    # We want to be able to use hasattr with the event dict properties.
+    # However, (on python3) hasattr expects AttributeError to be raised. Hence,
+    # we need to transform the KeyError into an AttributeError
     def getter(self):
-        return self._event_dict[key]
+        try:
+            return self._event_dict[key]
+        except KeyError:
+            raise AttributeError(key)
 
     def setter(self, v):
-        self._event_dict[key] = v
+        try:
+            self._event_dict[key] = v
+        except KeyError:
+            raise AttributeError(key)
 
     def delete(self):
-        del self._event_dict[key]
+        try:
+            del self._event_dict[key]
+        except KeyError:
+            raise AttributeError(key)
 
     return property(
         getter,