diff --git a/lib/helper.php b/lib/helper.php
index 5b3e394cafd3821195c5cd3ead775c045978827e..24d436225b7b9dba5d42abd64e2f3eac89d82a01 100644
--- a/lib/helper.php
+++ b/lib/helper.php
@@ -160,24 +160,25 @@ class OC_Helper {
 	 */
 	public static function computerFileSize( $str ){
 		$bytes = 0;
+		$str=strtolower($str);
 
 		$bytes_array = array(
-			'B' => 1,
-			'K' => 1024,
-			'KB' => 1024,
-			'MB' => 1024 * 1024,
-			'M'  => 1024 * 1024,
-			'GB' => 1024 * 1024 * 1024,
-			'G'  => 1024 * 1024 * 1024,
-			'TB' => 1024 * 1024 * 1024 * 1024,
-			'T'  => 1024 * 1024 * 1024 * 1024,
-			'PB' => 1024 * 1024 * 1024 * 1024 * 1024,
-			'P'  => 1024 * 1024 * 1024 * 1024 * 1024,
+			'b' => 1,
+			'k' => 1024,
+			'kb' => 1024,
+			'mb' => 1024 * 1024,
+			'm'  => 1024 * 1024,
+			'gb' => 1024 * 1024 * 1024,
+			'g'  => 1024 * 1024 * 1024,
+			'tb' => 1024 * 1024 * 1024 * 1024,
+			't'  => 1024 * 1024 * 1024 * 1024,
+			'pb' => 1024 * 1024 * 1024 * 1024 * 1024,
+			'p'  => 1024 * 1024 * 1024 * 1024 * 1024,
 		);
 
 		$bytes = floatval($str);
 
-		if (preg_match('#([KMGTP]?B?)$#si', $str, $matches) && !empty($bytes_array[$matches[1]])) {
+		if (preg_match('#([kmgtp]?b?)$#si', $str, $matches) && !empty($bytes_array[$matches[1]])) {
 			$bytes *= $bytes_array[$matches[1]];
 		}