diff --git a/src/BinPacker.php b/src/BinPacker.php
index 7e3b48c..835c092 100644
--- a/src/BinPacker.php
+++ b/src/BinPacker.php
@@ -144,7 +144,7 @@ public function growDown(Node $node, $w, $h)
     private function sort($blocks)
     {
         usort($blocks, function (Block $a, Block $b) {
-            return $a->getHeight() < $b->getHeight() ;
+            return $a->getHeight() < $b->getHeight() ? -1 : ($a->getHeight() === $b->getHeight() ? 0 : 1);
         });
 
         return $blocks;