diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
index 9600b1d0..7f48a6c1 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Worksheet.php
@@ -519,6 +519,9 @@ class Worksheet extends WriterPart
                             // Formula
                             $objWriter->writeElement('formula', $formula);
                         }
+                    } elseif ($conditional->getConditionType() == Conditional::CONDITION_CONTAINSBLANKS) {
+                        // formula copied from ms xlsx xml source file
+                        $objWriter->writeElement('formula', 'LEN(TRIM(' . $cellCoordinate . '))=0');
                     }
 
                     $objWriter->endElement();