diff --git a/changelog.d/10875.bugfix b/changelog.d/10875.bugfix
new file mode 100644
index 000000000..6f370da5c
--- /dev/null
+++ b/changelog.d/10875.bugfix
@@ -0,0 +1 @@
+Fix invalidating one-time key count cache after claiming keys. Contributed by Tulir at Beeper.
diff --git a/synapse/storage/databases/main/end_to_end_keys.py b/synapse/storage/databases/main/end_to_end_keys.py
index 1f0a39eac..a95ac34f0 100644
--- a/synapse/storage/databases/main/end_to_end_keys.py
+++ b/synapse/storage/databases/main/end_to_end_keys.py
@@ -824,6 +824,10 @@ class EndToEndKeyWorkerStore(EndToEndKeyBackgroundStore):
             if otk_row is None:
                 return None
 
+            self._invalidate_cache_and_stream(
+                txn, self.count_e2e_one_time_keys, (user_id, device_id)
+            )
+
             key_id, key_json = otk_row
             return f"{algorithm}:{key_id}", key_json