diff --git a/core/modules/system/src/Tests/File/NameMungingTest.php b/core/modules/system/src/Tests/File/NameMungingTest.php
index 9c0d3d9..4fa539e 100644
--- a/core/modules/system/src/Tests/File/NameMungingTest.php
+++ b/core/modules/system/src/Tests/File/NameMungingTest.php
@@ -60,8 +60,8 @@ function testMungeIgnoreInsecure() {
    * White listed extensions are ignored by file_munge_filename().
    */
   function testMungeIgnoreWhitelisted() {
-    // Declare our extension as whitelisted.
-    $munged_name = file_munge_filename($this->name, $this->bad_extension);
+    // Declare our extension as whitelisted. The declared extensions should be case insensitive so test using one with a different case.
+    $munged_name = file_munge_filename($this->name, strtoupper($this->bad_extension));
     $this->assertIdentical($munged_name, $this->name, format_string('The new filename (%munged) matches the original (%original) once the extension has been whitelisted.', array('%munged' => $munged_name, '%original' => $this->name)));
   }