diff --git a/synapse/api/events/__init__.py b/synapse/api/events/__init__.py
index 5f300de10..72c493db5 100644
--- a/synapse/api/events/__init__.py
+++ b/synapse/api/events/__init__.py
@@ -17,6 +17,18 @@ from synapse.api.errors import SynapseError, Codes
 from synapse.util.jsonobject import JsonEncodedObject
 
 
+def serialize_event(hs, e):
+    # FIXME(erikj): To handle the case of presence events and the like
+    if not isinstance(e, SynapseEvent):
+        return e
+
+    d = e.get_dict()
+    if "age_ts" in d:
+        d["age"] = int(hs.get_clock().time_msec()) - d["age_ts"]
+
+    return d
+
+
 class SynapseEvent(JsonEncodedObject):
 
     """Base class for Synapse events. These are JSON objects which must abide
@@ -43,6 +55,7 @@ class SynapseEvent(JsonEncodedObject):
         "content",  # HTTP body, JSON
         "state_key",
         "required_power_level",
+        "age_ts",
     ]
 
     internal_keys = [
diff --git a/synapse/api/events/factory.py b/synapse/api/events/factory.py
index 5e38cdbc4..d3d96d73e 100644
--- a/synapse/api/events/factory.py
+++ b/synapse/api/events/factory.py
@@ -59,6 +59,14 @@ class EventFactory(object):
         if "ts" not in kwargs:
             kwargs["ts"] = int(self.clock.time_msec())
 
+        # The "age" key is a delta timestamp that should be converted into an
+        # absolute timestamp the minute we see it.
+        if "age" in kwargs:
+            kwargs["age_ts"] = int(self.clock.time_msec()) - int(kwargs["age"])
+            del kwargs["age"]
+        elif "age_ts" not in kwargs:
+            kwargs["age_ts"] = int(self.clock.time_msec())
+
         if etype in self._event_list:
             handler = self._event_list[etype]
         else:
diff --git a/synapse/federation/replication.py b/synapse/federation/replication.py
index e12510017..c79ce4468 100644
--- a/synapse/federation/replication.py
+++ b/synapse/federation/replication.py
@@ -291,6 +291,12 @@ class ReplicationLayer(object):
     def on_incoming_transaction(self, transaction_data):
         transaction = Transaction(**transaction_data)
 
+        for p in transaction.pdus:
+            if "age" in p:
+                p["age_ts"] = int(self.clock.time_msec()) - int(p["age"])
+
+        pdu_list = [Pdu(**p) for p in transaction.pdus]
+
         logger.debug("[%s] Got transaction", transaction.transaction_id)
 
         response = yield self.transaction_actions.have_responded(transaction)
@@ -303,8 +309,6 @@ class ReplicationLayer(object):
 
         logger.debug("[%s] Transacition is new", transaction.transaction_id)
 
-        pdu_list = [Pdu(**p) for p in transaction.pdus]
-
         dl = []
         for pdu in pdu_list:
             dl.append(self._handle_new_pdu(pdu))
@@ -405,9 +409,14 @@ class ReplicationLayer(object):
         """Returns a new Transaction containing the given PDUs suitable for
         transmission.
         """
+        pdus = [p.get_dict() for p in pdu_list]
+        for p in pdus:
+            if "age_ts" in pdus:
+                p["age"] = int(self.clock.time_msec()) - p["age_ts"]
+
         return Transaction(
-            pdus=[p.get_dict() for p in pdu_list],
             origin=self.server_name,
+            pdus=pdus,
             ts=int(self._clock.time_msec()),
             destination=None,
         )
diff --git a/synapse/handlers/events.py b/synapse/handlers/events.py
index fd24a11fb..93dcd4032 100644
--- a/synapse/handlers/events.py
+++ b/synapse/handlers/events.py
@@ -15,7 +15,6 @@
 
 from twisted.internet import defer
 
-from synapse.api.events import SynapseEvent
 from synapse.util.logutils import log_function
 
 from ._base import BaseHandler
@@ -71,10 +70,7 @@ class EventStreamHandler(BaseHandler):
                 auth_user, room_ids, pagin_config, timeout
             )
 
-            chunks = [
-                e.get_dict() if isinstance(e, SynapseEvent) else e
-                for e in events
-            ]
+            chunks = [self.hs.serialize_event(e) for e in events]
 
             chunk = {
                 "chunk": chunks,
@@ -92,7 +88,9 @@ class EventStreamHandler(BaseHandler):
                 # 10 seconds of grace to allow the client to reconnect again
                 #   before we think they're gone
                 def _later():
-                    logger.debug("_later stopped_user_eventstream %s", auth_user)
+                    logger.debug(
+                        "_later stopped_user_eventstream %s", auth_user
+                    )
                     self.distributor.fire(
                         "stopped_user_eventstream", auth_user
                     )
diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py
index 87fc04478..b63863e5b 100644
--- a/synapse/handlers/message.py
+++ b/synapse/handlers/message.py
@@ -124,7 +124,7 @@ class MessageHandler(BaseHandler):
         )
 
         chunk = {
-            "chunk": [e.get_dict() for e in events],
+            "chunk": [self.hs.serialize_event(e) for e in events],
             "start": pagin_config.from_token.to_string(),
             "end": next_token.to_string(),
         }
@@ -296,7 +296,7 @@ class MessageHandler(BaseHandler):
                 end_token = now_token.copy_and_replace("room_key", token[1])
 
                 d["messages"] = {
-                    "chunk": [m.get_dict() for m in messages],
+                    "chunk": [self.hs.serialize_event(m) for m in messages],
                     "start": start_token.to_string(),
                     "end": end_token.to_string(),
                 }
@@ -304,7 +304,7 @@ class MessageHandler(BaseHandler):
                 current_state = yield self.store.get_current_state(
                     event.room_id
                 )
-                d["state"] = [c.get_dict() for c in current_state]
+                d["state"] = [self.hs.serialize_event(c) for c in current_state]
             except:
                 logger.exception("Failed to get snapshot")
 
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 310cb46fe..5bc128043 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -335,7 +335,7 @@ class RoomMemberHandler(BaseHandler):
 
         member_list = yield self.store.get_room_members(room_id=room_id)
         event_list = [
-            entry.get_dict()
+            self.hs.serialize_event(entry)
             for entry in member_list
         ]
         chunk_data = {
diff --git a/synapse/rest/events.py b/synapse/rest/events.py
index 7fde14320..097195d7c 100644
--- a/synapse/rest/events.py
+++ b/synapse/rest/events.py
@@ -59,7 +59,7 @@ class EventRestServlet(RestServlet):
         event = yield handler.get_event(auth_user, event_id)
 
         if event:
-            defer.returnValue((200, event.get_dict()))
+            defer.returnValue((200, self.hs.serialize_event(event)))
         else:
             defer.returnValue((404, "Event not found."))
 
diff --git a/synapse/rest/room.py b/synapse/rest/room.py
index cef700c81..ecb1e346d 100644
--- a/synapse/rest/room.py
+++ b/synapse/rest/room.py
@@ -378,7 +378,7 @@ class RoomTriggerBackfill(RestServlet):
         handler = self.handlers.federation_handler
         events = yield handler.backfill(remote_server, room_id, limit)
 
-        res = [event.get_dict() for event in events]
+        res = [self.hs.serialize_event(event) for event in events]
         defer.returnValue((200, res))
 
 
diff --git a/synapse/server.py b/synapse/server.py
index 83368ea5a..7c185537a 100644
--- a/synapse/server.py
+++ b/synapse/server.py
@@ -20,6 +20,7 @@
 
 # Imports required for the default HomeServer() implementation
 from synapse.federation import initialize_http_replication
+from synapse.api.events import serialize_event
 from synapse.api.events.factory import EventFactory
 from synapse.notifier import Notifier
 from synapse.api.auth import Auth
@@ -138,6 +139,9 @@ class BaseHomeServer(object):
         object."""
         return RoomID.from_string(s, hs=self)
 
+    def serialize_event(self, e):
+        return serialize_event(self, e)
+
 # Build magic accessors for every dependency
 for depname in BaseHomeServer.DEPENDENCIES:
     BaseHomeServer._make_dependency_method(depname)
diff --git a/synapse/storage/_base.py b/synapse/storage/_base.py
index 8deaaf93b..cf88bfc22 100644
--- a/synapse/storage/_base.py
+++ b/synapse/storage/_base.py
@@ -315,6 +315,10 @@ class SQLBaseStore(object):
         d["content"] = json.loads(d["content"])
         del d["unrecognized_keys"]
 
+        if "age_ts" not in d:
+            # For compatibility
+            d["age_ts"] = d["ts"] if "ts" in d else 0
+
         return self.event_factory.create_event(
             etype=d["type"],
             **d