diff --git a/data/api/client-server/definitions/m.oauth_params.yaml b/data/api/client-server/definitions/m.oauth_params.yaml
index d6e35dc1..cf64da8e 100644
--- a/data/api/client-server/definitions/m.oauth_params.yaml
+++ b/data/api/client-server/definitions/m.oauth_params.yaml
@@ -24,6 +24,7 @@ properties:
       A URL pointing to the homeserver's OAuth account management web UI
       where the user can approve the action. MUST be a valid URI with scheme
       `http://` or `https://`, the latter being RECOMMENDED.
+    pattern: "^https?://"
 example: {
     "url": "https://example.org/account/reset-cross-signing"
 }