diff --git a/lib/private/legacy/OC_Image.php b/lib/private/legacy/OC_Image.php
index 1e2791f62c917e17fab4ef2b3953861cf686d57d..3e9812c99f2e69fda3290e8e6687765721e2d02f 100644
--- a/lib/private/legacy/OC_Image.php
+++ b/lib/private/legacy/OC_Image.php
@@ -1211,7 +1211,7 @@ if (!function_exists('imagebmp')) {
 			} // RLE8
 			elseif ($compression == 1 && $bit == 8) {
 				for ($j = $height - 1; $j >= 0; $j--) {
-					$lastIndex = 0;
+					$lastIndex = null;
 					$sameNum = 0;
 					for ($i = 0; $i <= $width; $i++) {
 						$index = imagecolorat($im, $i, $j);