diff --git a/src/PhpSpreadsheet/Collection/Cells.php b/src/PhpSpreadsheet/Collection/Cells.php
index 80a43220..465a0698 100644
--- a/src/PhpSpreadsheet/Collection/Cells.php
+++ b/src/PhpSpreadsheet/Collection/Cells.php
@@ -259,7 +259,7 @@ class Cells
             $columnList[] = Coordinate::columnIndexFromString($c);
         }
 
-        return Coordinate::stringFromColumnIndex(max($columnList) + 1);
+        return Coordinate::stringFromColumnIndex(max($columnList));
     }
 
     /**