diff --git a/lib/Cake/Test/Case/Utility/ValidationTest.php b/lib/Cake/Test/Case/Utility/ValidationTest.php
index 0d0c947122b..02cda1dc428 100644
--- a/lib/Cake/Test/Case/Utility/ValidationTest.php
+++ b/lib/Cake/Test/Case/Utility/ValidationTest.php
@@ -2362,8 +2362,8 @@ public function testMimeType() {
 		$this->assertTrue(Validation::mimeType($image, array('image/gif')));
 		$this->assertTrue(Validation::mimeType(array('tmp_name' => $image), array('image/gif')));
 		$this->assertTrue(Validation::mimeType(array('tmp_name' => $image), '#image/.+#'));
+		$this->assertTrue(Validation::mimeType($image, array('image/GIF')));
 
-		$this->assertFalse(Validation::mimeType($image, array('image/GIF')));
 		$this->assertFalse(Validation::mimeType($image, array('image/png')));
 		$this->assertFalse(Validation::mimeType(array('tmp_name' => $image), array('image/png')));
 	}
diff --git a/lib/Cake/Utility/Validation.php b/lib/Cake/Utility/Validation.php
index daf3d5fd5eb..b15e00c0d38 100644
--- a/lib/Cake/Utility/Validation.php
+++ b/lib/Cake/Utility/Validation.php
@@ -948,6 +948,9 @@ public static function mimeType($check, $mimeTypes = array()) {
 			return self::_check($mime, $mimeTypes);
 		}
 
+		foreach ($mimeTypes as $key => $val) {
+			$mimeTypes[$key] = strtolower($val);
+		}
 		return in_array($mime, $mimeTypes);
 	}