Take a copy before prefilling, as it may be a frozendict

1 files changed, 1 insertions, 1 deletions

diff --git a/synapse/storage/state.py b/synapse/storage/state.py

index 03981f5d2b..85acf2ad1e 100644
--- a/synapse/storage/state.py
+++ b/synapse/storage/state.py
@@ -235,7 +235,7 @@ class StateStore(SQLBaseStore):
                 self._state_group_cache.update,
                 self._state_group_cache.sequence,
                 key=context.state_group,
-                value=context.current_state_ids,
+                value=dict(context.current_state_ids),
                 full=True,
             )