diff --git a/changelogs/client_server/newsfragments/1685.clarification b/changelogs/client_server/newsfragments/1685.clarification
new file mode 100644
index 00000000..9daf762e
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1685.clarification
@@ -0,0 +1 @@
+Clarify that read-receipts should be batched by thread as well as room.
diff --git a/content/client-server-api/modules/receipts.md b/content/client-server-api/modules/receipts.md
index 54c8c7cf..d8733e19 100644
--- a/content/client-server-api/modules/receipts.md
+++ b/content/client-server-api/modules/receipts.md
@@ -208,7 +208,7 @@ event when the user expands that thread.
 
 #### Server behaviour
 
-For efficiency, receipts SHOULD be batched into one event per room
+For efficiency, receipts SHOULD be batched into one event per room and thread
 before delivering them to clients.
 
 Some receipts are sent across federation as EDUs with type `m.receipt`. The