diff --git a/core/modules/system/templates/select.html.twig b/core/modules/system/templates/select.html.twig
index 3235c95..29ec1fe 100644
--- a/core/modules/system/templates/select.html.twig
+++ b/core/modules/system/templates/select.html.twig
@@ -48,16 +48,19 @@
       {% spaceless %}
         {# Cast key to a string. #}
         {% set key = "#{key}" %}
+
         {# The defined test accommodates cases where element['#value'] is null. #}
         {% set empty_choice = element['#value'] is empty and element['#multiple'] is not empty %}
         {% if element['#value'] is not defined %}
           {% set selected = false %}
         {% elseif element['#value'] is not iterable %}
           {% set selected = ("#{element['#value']}" is same as(key)) %}
-        {% elseif key in element['#value'] %}
-          {% set selected = true %}
+        {% elseif element['#value'] is iterable %}
+          {% set selected = (key in element['#value']) %}
         {% elseif empty_choice and key == '_none' %}
           {% set selected = true %}
+        {% else %}
+          {% set selected = false %}
         {% endif %}
         <option value="{{ key }}"{{ selected ? ' selected="selected"' : '' }}>{{ choice }}</option>
       {% endspaceless %}