diff --git a/synapse/events/validator.py b/synapse/events/validator.py
index f319072d3..47830aa98 100644
--- a/synapse/events/validator.py
+++ b/synapse/events/validator.py
@@ -15,6 +15,7 @@
 
 from synapse.types import EventID, RoomID, UserID
 from synapse.api.errors import SynapseError
+from synapse.api.constants import EventTypes, Membership
 
 
 class EventValidator(object):
@@ -23,14 +24,19 @@ class EventValidator(object):
         EventID.from_string(event.event_id)
         RoomID.from_string(event.room_id)
 
-        hasattr(event, "auth_events")
-        hasattr(event, "content")
-        hasattr(event, "hashes")
-        hasattr(event, "origin")
-        hasattr(event, "prev_events")
-        hasattr(event, "prev_events")
-        hasattr(event, "sender")
-        hasattr(event, "type")
+        required = [
+            # "auth_events",
+            "content",
+            # "hashes",
+            "origin",
+            # "prev_events",
+            "sender",
+            "type",
+        ]
+
+        for k in required:
+            if not hasattr(event, k):
+                raise SynapseError(400, "Event does not have key %s" % (k,))
 
         # Check that the following keys have string values
         strings = [
@@ -46,6 +52,13 @@ class EventValidator(object):
             if not isinstance(getattr(event, s), basestring):
                 raise SynapseError(400, "Not '%s' a string type" % (s,))
 
+        if event.type == EventTypes.Member:
+            if "membership" not in event.content:
+                raise SynapseError(400, "Content has not membership key")
+
+            if event.content["membership"] not in Membership.LIST:
+                raise SynapseError(400, "Invalid membership key")
+
         # Check that the following keys have dictionary values
         # TODO
 
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 9043b945e..f92b01a50 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -19,6 +19,9 @@ from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import RoomError
 from synapse.streams.config import PaginationConfig
 from synapse.util.logcontext import PreserveLoggingContext
+
+from synapse.events.validator import EventValidator
+
 from ._base import BaseHandler
 
 import logging
@@ -33,6 +36,7 @@ class MessageHandler(BaseHandler):
         self.hs = hs
         self.clock = hs.get_clock()
         self.event_factory = hs.get_event_factory()
+        self.validator = EventValidator()
 
     @defer.inlineCallbacks
     def get_message(self, msg_id=None, room_id=None, sender_id=None,
@@ -137,6 +141,8 @@ class MessageHandler(BaseHandler):
     def handle_event(self, event_dict):
         builder = self.event_builder_factory.new(event_dict)
 
+        self.validator.validate(builder)
+
         if builder.type == EventTypes.Member:
             membership = builder.content.get("membership", None)
             if membership == Membership.JOIN:
@@ -152,8 +158,6 @@ class MessageHandler(BaseHandler):
             builder=builder,
         )
 
-        # TODO: self.validator.validate(event)
-
         if event.type == EventTypes.Member:
             member_handler = self.hs.get_handlers().room_member_handler
             yield member_handler.change_membership(event, context)