diff --git a/src/Spout/Writer/Common/Manager/ManagesCellSize.php b/src/Spout/Writer/Common/Manager/ManagesCellSize.php
index 44cf2a1..60de4cf 100644
--- a/src/Spout/Writer/Common/Manager/ManagesCellSize.php
+++ b/src/Spout/Writer/Common/Manager/ManagesCellSize.php
@@ -13,7 +13,7 @@ trait ManagesCellSize
     private $defaultRowHeight;
 
     /** @var array Array of min-max-width arrays */
-    private $columnWidths;
+    private $columnWidths = [];
 
     /**
      * @param float|null $width