diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index b10df59565..313d7216ba 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -3825,7 +3825,7 @@ private function readLabelSst()
                 }
             }
 
-            if (!$this->readDataOnly && !$emptyCell) {
+            if (!$this->readDataOnly && !$emptyCell && isset($this->mapCellXfIndex[$xfIndex])) {
                 // add style information
                 $cell->setXfIndex($this->mapCellXfIndex[$xfIndex]);
             }