diff --git a/calendar/providers/storage/CalStorageCachedItemModel.jsm b/calendar/providers/storage/CalStorageCachedItemModel.jsm
index f32c6b20a4..e4a721f49b 100644
--- a/calendar/providers/storage/CalStorageCachedItemModel.jsm
+++ b/calendar/providers/storage/CalStorageCachedItemModel.jsm
@@ -99,6 +99,7 @@ class CalStorageCachedItemModel extends CalStorageItemModel {
       // already waiting and we don't want to break that by throwing away the caches. If it IS
       // complete, we'll continue immediately.
       await this.mRecItemCachePromise;
+      await new Promise(resolve => ChromeUtils.idleDispatch(resolve));
       this.mRecItemCachePromise = null;
     }
     await this.assureRecurringItemCaches();