2 files changed, 6 insertions, 3 deletions
diff --git a/changelog.d/12496.bugfix b/changelog.d/12496.bugfix
new file mode 100644
index 0000000000..a68df7c96a
--- /dev/null
+++ b/changelog.d/12496.bugfix
@@ -0,0 +1 @@
+Fix bug where the admin API for [deleting forward extremities](https://github.com/matrix-org/synapse/blob/erikj/fix_delete_event_response_count/docs/admin_api/rooms.md#deleting-forward-extremities) would always return a count of 1 no matter how many extremities were deleted. Broke in v1.27.0.
diff --git a/synapse/storage/databases/main/events_forward_extremities.py b/synapse/storage/databases/main/events_forward_extremities.py
index 68901b4335..f851bff604 100644
--- a/synapse/storage/databases/main/events_forward_extremities.py
+++ b/synapse/storage/databases/main/events_forward_extremities.py
@@ -66,13 +66,15 @@ class EventForwardExtremitiesStore(
             """
 
             txn.execute(sql, (event_id, room_id))
+
+            deleted_count = txn.rowcount
             logger.info(
                 "Deleted %s extra forward extremities for room %s",
-                txn.rowcount,
+                deleted_count,
                 room_id,
             )
 
-            if txn.rowcount > 0:
+            if deleted_count > 0:
                 # Invalidate the cache
                 self._invalidate_cache_and_stream(
                     txn,
@@ -80,7 +82,7 @@ class EventForwardExtremitiesStore(
                     (room_id,),
                 )
 
-            return txn.rowcount
+            return deleted_count
 
         return await self.db_pool.runInteraction(
             "delete_forward_extremities_for_room",