diff --git a/core/lib/Drupal/Core/Template/TwigEnvironment.php b/core/lib/Drupal/Core/Template/TwigEnvironment.php
index 8118105..8828496 100644
--- a/core/lib/Drupal/Core/Template/TwigEnvironment.php
+++ b/core/lib/Drupal/Core/Template/TwigEnvironment.php
@@ -131,6 +131,14 @@ public function loadTemplate($name, $index = NULL) {
           $this->updateCompiledTemplate($cache_filename, $name);
           $this->storage()->load($cache_filename);
         }
+
+        if (!class_exists($cls, FALSE)) {
+          // In some rare race conditions with concurrent requests, we might
+          // have failed load load the class. In that case, execute the code
+          // directly to make the class available.
+          $compiled_source = $this->compileSource($this->loader->getSource($name), $name);
+          eval('?' . '>' . $compiled_source);
+        }
       }
     }