diff --git a/changelog.d/9915.feature b/changelog.d/9915.feature
new file mode 100644
index 000000000000..832916cb01af
--- /dev/null
+++ b/changelog.d/9915.feature
@@ -0,0 +1 @@
+Support stable identifiers from [MSC1772](https://github.com/matrix-org/matrix-doc/pull/1772).
diff --git a/synapse/api/constants.py b/synapse/api/constants.py
index 936b6534b41f..622d628f679f 100644
--- a/synapse/api/constants.py
+++ b/synapse/api/constants.py
@@ -110,6 +110,8 @@ class EventTypes:
 
     Dummy = "org.matrix.dummy_event"
 
+    SpaceChild = "m.space.child"
+    SpaceParent = "m.space.parent"
     MSC1772_SPACE_CHILD = "org.matrix.msc1772.space.child"
     MSC1772_SPACE_PARENT = "org.matrix.msc1772.space.parent"
 
diff --git a/synapse/handlers/space_summary.py b/synapse/handlers/space_summary.py
index 01e3e050f93c..38c682a838cb 100644
--- a/synapse/handlers/space_summary.py
+++ b/synapse/handlers/space_summary.py
@@ -288,6 +288,7 @@ async def _summarize_remote_room(
             ev.data
             for ev in res.events
             if ev.event_type == EventTypes.MSC1772_SPACE_CHILD
+            or ev.event_type == EventTypes.SpaceChild
         )
 
     async def _is_room_accessible(self, room_id: str, requester: Optional[str]) -> bool:
@@ -360,8 +361,9 @@ async def _get_child_events(self, room_id: str) -> Iterable[EventBase]:
             [
                 event_id
                 for key, event_id in current_state_ids.items()
-                # TODO: update once MSC1772 lands
+                # TODO: update once MSC1772 has been FCP for a period of time.
                 if key[0] == EventTypes.MSC1772_SPACE_CHILD
+                or key[0] == EventTypes.SpaceChild
             ]
         )