diff --git a/changelog.d/8530.bugfix b/changelog.d/8530.bugfix
new file mode 100644
index 0000000000..443d88424e
--- /dev/null
+++ b/changelog.d/8530.bugfix
@@ -0,0 +1 @@
+Fix rare bug where sending an event would fail due to a racey assertion.
diff --git a/synapse/storage/util/id_generators.py b/synapse/storage/util/id_generators.py
index ad017207aa..eccd2d5b7b 100644
--- a/synapse/storage/util/id_generators.py
+++ b/synapse/storage/util/id_generators.py
@@ -612,14 +612,7 @@ class _MultiWriterCtxManager:
             db_autocommit=True,
         )
 
-        # Assert the fetched ID is actually greater than any ID we've already
-        # seen. If not, then the sequence and table have got out of sync
-        # somehow.
         with self.id_gen._lock:
-            assert max(self.id_gen._current_positions.values(), default=0) < min(
-                self.stream_ids
-            )
-
             self.id_gen._unfinished_ids.update(self.stream_ids)
 
         if self.multiple_ids is None: