diff --git a/changelog.d/3712.misc b/changelog.d/3712.misc
new file mode 100644
index 000000000..30f8c2af2
--- /dev/null
+++ b/changelog.d/3712.misc
@@ -0,0 +1 @@
+Update admin register API documentation to reference a real user ID.
diff --git a/docs/admin_api/register_api.rst b/docs/admin_api/register_api.rst
index 209cd140f..16d65c86b 100644
--- a/docs/admin_api/register_api.rst
+++ b/docs/admin_api/register_api.rst
@@ -33,7 +33,7 @@ As an example::
 
   < {
      "access_token": "token_here",
-     "user_id": "@pepper_roni@test",
+     "user_id": "@pepper_roni:localhost",
      "home_server": "test",
      "device_id": "device_id_here"
     }