diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index d2fe902..7ae9893 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1383,11 +1383,11 @@ function theme_get_setting($setting_name, $theme = NULL) {
     }
 
     // Get the saved global settings from the database.
-    $cache[$theme] = array_merge($cache[$theme], variable_get('theme_settings', array()));
+    $cache[$theme] = array_merge($cache[$theme], config('system.theme')->get('theme_settings') ?: array());
 
     if ($theme) {
       // Get the saved theme-specific settings from the database.
-      $cache[$theme] = array_merge($cache[$theme], variable_get('theme_' . $theme . '_settings', array()));
+      $cache[$theme] = array_merge($cache[$theme], config('system.theme')->get('theme_' . $theme . '_settings') ?: array());
 
       // If the theme does not support a particular feature, override the global
       // setting and set the value to NULL.
diff --git a/core/modules/system/system.admin.inc b/core/modules/system/system.admin.inc
index c55289c..165e52c 100644
--- a/core/modules/system/system.admin.inc
+++ b/core/modules/system/system.admin.inc
@@ -732,7 +732,7 @@ function system_theme_settings_submit($form, &$form_state) {
     }
   }
 
-  variable_set($key, $values);
+  config('system.theme')->set($key, $values)->save();
   drupal_set_message(t('The configuration options have been saved.'));
 
   cache_invalidate(array('content' => TRUE));
diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 25c7adb..fba9102 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -2214,6 +2214,17 @@ function system_update_8033() {
 }
 
 /**
+ * Converts theme_settings variable to config.
+ *
+ * @ingroup config_upgrade
+ */
+function system_update_8034() {
+  update_variables_to_config('system.theme', array(
+    'theme_settings' => 'theme_settings'
+  ));
+}
+
+/**
  * @} End of "defgroup updates-7.x-to-8.x".
  * The next series of updates should start at 9000.
  */