diff --git a/api/client-server/room_state.yaml b/api/client-server/room_state.yaml
index c04fb803..bda66eb8 100644
--- a/api/client-server/room_state.yaml
+++ b/api/client-server/room_state.yaml
@@ -87,6 +87,16 @@ paths:
                 type: string
                 description: |-
                   A unique identifier for the event.
+        403:
+          description: |-
+            The sender doesn't have permission to send the event into the room.
+          schema:
+            $ref: "definitions/errors/error.yaml"
+          examples:
+            application/json: {
+              "errcode": "M_FORBIDDEN",
+              "error": "You do not have permission to send the event."
+            }
       tags:
         - Room participation
   "/rooms/{roomId}/state/{eventType}":
@@ -142,5 +152,15 @@ paths:
                 type: string
                 description: |-
                   A unique identifier for the event.
+        403:
+          description: |-
+            The sender doesn't have permission to send the event into the room.
+          schema:
+            $ref: "definitions/errors/error.yaml"
+          examples:
+            application/json: {
+              "errcode": "M_FORBIDDEN",
+              "error": "You do not have permission to send the event."
+            }
       tags:
         - Room participation
diff --git a/changelogs/client_server/newsfragments/1590.clarification b/changelogs/client_server/newsfragments/1590.clarification
new file mode 100644
index 00000000..27999193
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1590.clarification
@@ -0,0 +1 @@
+Document the 403 error for sending state events.