diff --git a/crates/matrix-sdk/src/event_cache/caches/thread/state.rs b/crates/matrix-sdk/src/event_cache/caches/thread/state.rs
index af2fbfa9e..b2e27a243 100644
--- a/crates/matrix-sdk/src/event_cache/caches/thread/state.rs
+++ b/crates/matrix-sdk/src/event_cache/caches/thread/state.rs
@@ -278,6 +278,7 @@ impl<'a> ThreadEventCacheStateLockWriteGuard<'a> {
         Ok(())
     }
 
+    #[must_use = "Propagate `VectorDiff` updates via `TimelineVectorDiffs`"]
     pub async fn handle_sync(&mut self, events: Vec<Event>) -> Result<Vec<VectorDiff<Event>>> {
         let DeduplicationOutcome {
             all_events: events,