diff --git a/filesystem/File.php b/filesystem/File.php
index 961c48b7d..f636edce9 100755
--- a/filesystem/File.php
+++ b/filesystem/File.php
@@ -770,8 +770,9 @@ class File extends DataObject {
 			// Extension validation
 			// TODO Merge this with Upload_Validator
 			$extension = $this->getExtension();
-			if($extension && !in_array($extension, self::$allowed_extensions)) {
-				$exts =  self::$allowed_extensions;
+			$allowed = array_map('strtolower', self::$allowed_extensions);
+			if($extension && !in_array(strtolower($extension), $allowed)) {
+				$exts =  $allowed;
 				sort($exts);
 				$message = sprintf(
 					_t(
diff --git a/tests/filesystem/FileTest.php b/tests/filesystem/FileTest.php
index 0f62ab7ed..4d2adebde 100644
--- a/tests/filesystem/FileTest.php
+++ b/tests/filesystem/FileTest.php
@@ -60,6 +60,11 @@ class FileTest extends SapphireTest {
 		$v = $file->validate();
 		$this->assertTrue($v->valid());
 		
+		// Capital extension is valid as well
+		$file->Name = 'asdf.TXT';
+		$v = $file->validate();
+		$this->assertTrue($v->valid());
+		
 		File::$allowed_extensions = $origExts;
 	}