diff --git a/src/pocketmine/level/generator/populator/GroundCover.php b/src/pocketmine/level/generator/populator/GroundCover.php
index 08cd1c5d2..7858bd2dc 100644
--- a/src/pocketmine/level/generator/populator/GroundCover.php
+++ b/src/pocketmine/level/generator/populator/GroundCover.php
@@ -47,13 +47,13 @@ class GroundCover extends Populator{
 					}
 
 					$column = $chunk->getBlockIdColumn($x, $z);
-					$y = 127;
-					for(; $y > 0; --$y){
-						if($column[$y] !== "\x00" and !BlockFactory::get(ord($column[$y]))->isTransparent()){
+					$startY = 127;
+					for(; $startY > 0; --$startY){
+						if($column[$startY] !== "\x00" and !BlockFactory::get(ord($column[$startY]))->isTransparent()){
 							break;
 						}
 					}
-					$startY = min(127, $y + $diffY);
+					$startY = min(127, $startY + $diffY);
 					$endY = $startY - count($cover);
 					for($y = $startY; $y > $endY and $y >= 0; --$y){
 						$b = $cover[$startY - $y];