diff --git a/book/changelog.md b/book/changelog.md
index 70af61f4..6dfe833b 100644
--- a/book/changelog.md
+++ b/book/changelog.md
@@ -220,6 +220,11 @@ This will be the first release of Grapevine since it was forked from Conduit
     so this situation is common.
     ([!55](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/55))
     ([!153](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/153))
+25. Return 400 M_BAD_ALIAS from
+    [PUT /_matrix/client/v3/rooms/{roomId}/state/{eventType}/{stateKey}](https://spec.matrix.org/latest/client-server-api/#put_matrixclientv3roomsroomidstateeventtypestatekey)
+    instead of 400 M_FORBIDDEN when trying to set a canonical alias that does
+    not exist.
+    ([!158](https://gitlab.computer.surgery/matrix/grapevine/-/merge_requests/158))
 
 ### Added
 
diff --git a/src/api/client_server/state.rs b/src/api/client_server/state.rs
index b0e5809a..a9a6c0fc 100644
--- a/src/api/client_server/state.rs
+++ b/src/api/client_server/state.rs
@@ -232,7 +232,7 @@ async fn send_state_event_for_key_helper(
                     .is_none()
             {
                 return Err(Error::BadRequest(
-                    ErrorKind::forbidden(),
+                    ErrorKind::BadAlias,
                     "You are only allowed to send canonical_alias events when \
                      it's aliases already exists",
                 ));