diff --git a/core/tests/Drupal/KernelTests/Core/Theme/TwigEnvironmentTest.php b/core/tests/Drupal/KernelTests/Core/Theme/TwigEnvironmentTest.php
index c3e7af6..12bfd73 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/TwigEnvironmentTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/TwigEnvironmentTest.php
@@ -116,6 +116,20 @@ public function testCacheFilename() {
     // static cache.
     $environment = \Drupal::service('twig');
 
+    // A template basename greater than the constant
+    // TwigPhpStorageCache::SUFFIX_SUBSTRING_LENGTH should get truncated.
+    $cache = $environment->getCache();
+    $long_name = 'core/modules/system/templates/block--system-messages-block.html.twig';
+    $this->assertGreaterThan(TwigPhpStorageCache::SUFFIX_SUBSTRING_LENGTH, strlen(basename($long_name)));
+    $class = $environment->getTemplateClass($long_name);
+    $key = $cache->generateKey($long_name, $class);
+    $prefix = $environment->getTwigCachePrefix();
+    // The key should consist of the prefix, an underscore, and two strings
+    // each truncated to length TwigPhpStorageCache::SUFFIX_SUBSTRING_LENGTH
+    // separated by an underscore.
+    $expected = strlen($prefix) + 2 + 2 * TwigPhpStorageCache::SUFFIX_SUBSTRING_LENGTH;
+    $this->assertEquals($expected, strlen($key));
+
     $original_filename = $environment->getCacheFilename('core/modules/system/templates/container.html.twig');
     \Drupal::getContainer()->set('twig', NULL);