diff --git a/upload.php b/upload.php
index 9348e6c..0867b52 100644
--- a/upload.php
+++ b/upload.php
@@ -12,6 +12,7 @@ if(!is_dir($datadir)) {
 
 if(isset($_FILES['upload'])) {
 	$extension = pathinfo($_FILES['upload']['name'], PATHINFO_EXTENSION);
+	$extension = strtolower($extension);
 
 	if($extension == 'jpg' || $extension == 'jpeg' || $extension == 'png') {
 		$filename = generate_filename($length) . '.' . $extension;