diff -u b/src/Element/Country.php b/src/Element/Country.php
--- b/src/Element/Country.php
+++ b/src/Element/Country.php
@@ -87,7 +87,8 @@
     // Rebuild country options if any preferred countries have been selected.
     // @todo In the views filter, preferred countries are an associative array
     //   which is nicer to handle. See if this can be further streamlined.
-    $preferred_countries = array_combine($element['#preferred_countries'], $element['#preferred_countries']);
+    $preferred_countries = $element['#preferred_countries'] ?? [];
+    $preferred_countries = array_combine($preferred_countries, $preferred_countries);
     $country_options = empty($preferred_countries) ? $country_list : self::rebuildCountryList($country_list, $preferred_countries);
 
     // Hide the dropdown when there is only one possible value.