diff --git a/api/client-server/sync.yaml b/api/client-server/sync.yaml
index 02fddb84..4514d417 100644
--- a/api/client-server/sync.yaml
+++ b/api/client-server/sync.yaml
@@ -167,11 +167,13 @@ paths:
                             this room.
                           allOf:
                           - $ref: "definitions/event_batch.yaml"
-                        "unread_notifications":
+                        unread_notifications:
                           title: Unread Notification Counts
                           type: object
                           description: |-
-                            Counts of unread notifications for this room
+                            Counts of unread notifications for this room. See the
+                            `Receipts module <#module-receipts>`_ for more information
+                            on how these are calculated.
                           properties:
                             highlight_count:
                                 title: Highlighted notification count
diff --git a/changelogs/client_server/newsfragments/2097.clarification b/changelogs/client_server/newsfragments/2097.clarification
new file mode 100644
index 00000000..68d89bcc
--- /dev/null
+++ b/changelogs/client_server/newsfragments/2097.clarification
@@ -0,0 +1 @@
+Clarify how ``unread_notifications`` is calculated.
diff --git a/specification/modules/receipts.rst b/specification/modules/receipts.rst
index ee2b697a..1745706e 100644
--- a/specification/modules/receipts.rst
+++ b/specification/modules/receipts.rst
@@ -26,7 +26,9 @@ to a homeserver. To prevent this from becoming a problem, receipts are implement
 using "up to" markers. This marker indicates that the acknowledgement applies
 to all events "up to and including" the event specified. For example, marking
 an event as "read" would indicate that the user had read all events *up to* the
-referenced event.
+referenced event. Servers MUST decremement the number of pending notifications
+for a user if the events are up to or including the read receipt. This is typically
+done by adjusting the ``unread_notifications`` value in a ``/sync`` response.
 
 Events
 ------