diff --git a/core/lib/Drupal/Core/Extension/ThemeHandler.php b/core/lib/Drupal/Core/Extension/ThemeHandler.php
index d54ff1f..3101dcc 100644
--- a/core/lib/Drupal/Core/Extension/ThemeHandler.php
+++ b/core/lib/Drupal/Core/Extension/ThemeHandler.php
@@ -474,6 +474,7 @@ public function getThemeDirectories() {
    * {@inheritdoc}
    */
   public function themeExists($theme) {
+    $this->rebuildThemeData();
     $themes = $this->listInfo();
     return isset($themes[$theme]);
   }