diff --git a/TestResponse.php b/TestResponse.php
index f391bc7..4c5939f 100644
--- a/TestResponse.php
+++ b/TestResponse.php
@@ -373,7 +373,7 @@ public function assertHeader($headerName, $value = null)
         $actual = $this->headers->get($headerName);
 
         if (! is_null($value)) {
-            PHPUnit::withResponse($this)->assertEquals(
+            PHPUnit::withResponse($this)->assertEqualsIgnoringCase(
                 $value, $this->headers->get($headerName),
                 "Header [{$headerName}] was found, but value [{$actual}] does not match [{$value}]."
             );