diff --git a/Classes/PHPExcel/Writer/HTML.php b/Classes/PHPExcel/Writer/HTML.php
index 5dcb998..8fd6255 100644
--- a/Classes/PHPExcel/Writer/HTML.php
+++ b/Classes/PHPExcel/Writer/HTML.php
@@ -398,7 +398,7 @@ class PHPExcel_Writer_HTML extends PHPExcel_Writer_Abstract implements PHPExcel_
         }
 
         // Ensure that Spans have been calculated?
-        if (!$this->spansAreCalculated) {
+        if ($this->_sheetIndex !== null || !$this->spansAreCalculated) {
             $this->calculateSpans();
         }