diff --git a/synapse/storage/receipts.py b/synapse/storage/receipts.py
index 33fc2b9b3..0ac665e96 100644
--- a/synapse/storage/receipts.py
+++ b/synapse/storage/receipts.py
@@ -163,7 +163,7 @@ class ReceiptsWorkerStore(SQLBaseStore):
                 from the start.
 
         Returns:
-            list: A list of receipts.
+            Deferred[list]: A list of receipts.
         """
         if from_key is not None:
             # Check the cache first to see if any new receipts have been added