diff --git a/changelog.d/19402.misc b/changelog.d/19402.misc
new file mode 100644
index 00000000000..0e1ee104a78
--- /dev/null
+++ b/changelog.d/19402.misc
@@ -0,0 +1 @@
+Don't retry joining partial state rooms all at once on startup.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 7808f8928b0..14805ac80f7 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1788,6 +1788,10 @@ async def _resume_partial_state_room_sync(self) -> None:
                 room_id=room_id,
             )
 
+            # We don't start all the partial state room syncs at once, to avoid
+            # overloading the process.
+            await self.clock.sleep(Duration(milliseconds=10))
+
     def _start_partial_state_room_sync(
         self,
         initial_destination: str | None,