diff --git a/changelog.d/3589.feature b/changelog.d/3589.feature
new file mode 100644
index 0000000000..a8d7124719
--- /dev/null
+++ b/changelog.d/3589.feature
@@ -0,0 +1 @@
+Add lazy-loading support to /messages as per MSC1227
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index a97d43550f..5170d093e3 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -18,7 +18,7 @@ import logging
 from twisted.internet import defer
 from twisted.python.failure import Failure
 
-from synapse.api.constants import Membership
+from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import SynapseError
 from synapse.events.utils import serialize_event
 from synapse.types import RoomStreamToken
@@ -251,6 +251,33 @@ class PaginationHandler(object):
             is_peeking=(member_event_id is None),
         )
 
+        state = None
+        if event_filter and event_filter.lazy_load_members():
+            # TODO: remove redundant members
+
+            types = [
+                (EventTypes.Member, state_key)
+                for state_key in set(
+                    event.sender  # FIXME: we also care about invite targets etc.
+                    for event in events
+                )
+            ]
+
+            state_ids = yield self.store.get_state_ids_for_event(
+                events[0].event_id, types=types,
+            )
+
+            if state_ids:
+                state = yield self.store.get_events(list(state_ids.values()))
+
+            if state:
+                state = yield filter_events_for_client(
+                    self.store,
+                    user_id,
+                    state.values(),
+                    is_peeking=(member_event_id is None),
+                )
+
         time_now = self.clock.time_msec()
 
         chunk = {
@@ -262,4 +289,10 @@ class PaginationHandler(object):
             "end": next_token.to_string(),
         }
 
+        if state:
+            chunk["state"] = [
+                serialize_event(e, time_now, as_client_event)
+                for e in state
+            ]
+
         defer.returnValue(chunk)
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 6ac2987b98..29e62bfcdd 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -27,11 +27,22 @@ class VersionsRestServlet(RestServlet):
     def on_GET(self, request):
         return (200, {
             "versions": [
+                # XXX: at some point we need to decide whether we need to include
+                # the previous version numbers, given we've defined r0.3.0 to be
+                # backwards compatible with r0.2.0.  But need to check how
+                # conscientious we've been in compatibility, and decide whether the
+                # middle number is the major revision when at 0.X.Y (as opposed to
+                # X.Y.Z).  And we need to decide whether it's fair to make clients
+                # parse the version string to figure out what's going on.
                 "r0.0.1",
                 "r0.1.0",
                 "r0.2.0",
                 "r0.3.0",
-            ]
+            ],
+            # as per MSC1497:
+            "unstable_features": {
+                "m.lazy_load_members": True,
+            }
         })