diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 6c5aaa3..6c49dc8 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -127,6 +127,11 @@ public function getCacheFilename($name) {
     $class = substr($this->getTemplateClass($name), strlen($this->templateClassPrefix));
 
     // The first part is what is invalidated.
+    if (!file_exists($name)) {
+      // $name is probably an inline template, and can have characters
+      // that are not valid for a filename.
+      $name = 'inline-template-' . sha1($name);
+    }
     return $this->templateCacheFilenamePrefix . '_' . basename($name) . '_' . $class;
   }