diff --git a/changelogs/client_server/newsfragments/1899.clarification b/changelogs/client_server/newsfragments/1899.clarification
new file mode 100644
index 00000000..6edeff05
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1899.clarification
@@ -0,0 +1 @@
+Clarify that the fallback login page calls `window.matrixLogin.onLogin` instead of `window.onLogin`.
diff --git a/content/client-server-api/_index.md b/content/client-server-api/_index.md
index 9558d536..be9a2384 100644
--- a/content/client-server-api/_index.md
+++ b/content/client-server-api/_index.md
@@ -1401,7 +1401,7 @@ fallback login API:
 
 This returns an HTML and JavaScript page which can perform the entire
 login process. The page will attempt to call the JavaScript function
-`window.onLogin` when login has been successfully completed.
+`window.matrixLogin.onLogin` when login has been successfully completed.
 
 {{% added-in v="1.1" %}} Non-credential parameters valid for the `/login`
 endpoint can be provided as query string parameters here. These are to be