diff --git a/core/lib/Drupal/Component/Utility/Twig.php b/core/lib/Drupal/Component/Utility/Twig.php
index 9a749ae..42fb23d 100644
--- a/core/lib/Drupal/Component/Utility/Twig.php
+++ b/core/lib/Drupal/Component/Utility/Twig.php
@@ -34,10 +34,11 @@ public static function isValidVariable($variable) {
    *   The variable to be tested.
    */
   public static function assertValidVariable($variable, $message = '') {
-    if (empty($message)) {
-      $message = '"' . Html::escape($variable) . '" is not a valid Twig variable.';
-    }
-    assert(Twig::isValidVariable($variable), $message);
+    // Asserts passed as a string are not evaluated when assertion checking
+    // is off. This allows us to skip the expensive preg_match() in
+    // isValidVariable when not running in dev. Also, we need the fully
+    // qualified namespace as the string is evaluated in assert's namespace.
+    assert('\Drupal\Component\Utility\Twig::isValidVariable($variable)', $message ?: '"' . Html::escape($variable) . '" is not a valid Twig variable.');
   }
 
 }
diff --git a/core/modules/views/src/Tests/Plugin/PluginBaseTest.php b/core/modules/views/src/Tests/Plugin/PluginBaseTest.php
index 60359e8..cf9534c 100644
--- a/core/modules/views/src/Tests/Plugin/PluginBaseTest.php
+++ b/core/modules/views/src/Tests/Plugin/PluginBaseTest.php
@@ -93,6 +93,7 @@ public function testViewsInvalidTokens() {
       \Drupal::service('renderer')->executeInRenderContext(new RenderContext(), function () use ($text, $tokens) {
         return $this->testPluginBase->viewsTokenReplace($text, $tokens);
       });
+      $this->fail('Failed to assert that "foo-bar" is an illegal Twig variable.');
     }
     catch(\Exception $e) {
       $this->assertIdentical('"foo-bar" is not a valid Twig variable.', $e->getMessage());