diff --git a/README.md b/README.md
index cc3ab2c2..cf86f37f 100644
--- a/README.md
+++ b/README.md
@@ -181,6 +181,9 @@ For a good example, see https://riot.im/develop/config.json.
     1. `homeUrl`: Content shown on the inside of the app when a specific room is
        not selected. By default, no home page is configured. If one is set, a
        button to access it will be shown in the top left menu.
+1. `defaultCountryCode`: The ISO 3166 alpha2 country code to use when showing
+   country selectors, like the phone number input on the registration page.
+   Defaults to `GB` if the given code is unknown or not provided.
 
 
 Note that `index.html` also has an og:image meta tag that is set to an image
diff --git a/config.sample.json b/config.sample.json
index db1d25d1..55bf12c3 100644
--- a/config.sample.json
+++ b/config.sample.json
@@ -18,6 +18,7 @@
     "integrations_rest_url": "https://scalar.vector.im/api",
     "integrations_jitsi_widget_url": "https://scalar.vector.im/api/widgets/jitsi.html",
     "bug_report_endpoint_url": "https://riot.im/bugreports/submit",
+    "defaultCountryCode": "GB",
     "showLabsSettings": false,
     "features": {
         "feature_groups": "labs",