diff --git a/core/lib/Drupal/Component/PhpStorage/MTimeProtectedFastFileStorage.php b/core/lib/Drupal/Component/PhpStorage/MTimeProtectedFastFileStorage.php
index ff1949418f..e18f012ef1 100644
--- a/core/lib/Drupal/Component/PhpStorage/MTimeProtectedFastFileStorage.php
+++ b/core/lib/Drupal/Component/PhpStorage/MTimeProtectedFastFileStorage.php
@@ -132,7 +132,7 @@ public function getFullPath($name, &$directory = NULL, &$directory_mtime = NULL)
     if (!isset($directory_mtime)) {
       $directory_mtime = file_exists($directory) ? filemtime($directory) : 0;
     }
-    return $directory . '/' . Crypt::hmacBase64($name, $this->secret . $directory_mtime) . '.php';
+    return $directory . '/' . Crypt::hmacBase64($name, $this->secret . $directory_mtime) . '.inc';
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Component/PhpStorage/MTimeProtectedFileStorageBase.php b/core/tests/Drupal/Tests/Component/PhpStorage/MTimeProtectedFileStorageBase.php
index cd68de55a3..df420edb64 100644
--- a/core/tests/Drupal/Tests/Component/PhpStorage/MTimeProtectedFileStorageBase.php
+++ b/core/tests/Drupal/Tests/Component/PhpStorage/MTimeProtectedFileStorageBase.php
@@ -86,7 +86,7 @@ public function testSecurity() {
       $expected_directory = $expected_root_directory . '/' . $name;
     }
     $directory_mtime = filemtime($expected_directory);
-    $expected_filename = $expected_directory . '/' . Crypt::hmacBase64($name, $this->secret . $directory_mtime) . '.php';
+    $expected_filename = $expected_directory . '/' . Crypt::hmacBase64($name, $this->secret . $directory_mtime) . '.inc';
 
     // Ensure the file exists and that it and the containing directory have
     // minimal permissions. fileperms() can return high bits unrelated to