diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73beb51c..60f3ef63 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -19,6 +19,7 @@ and this project adheres to [Semantic Versioning](https://semver.org).
 - Fix print area parser for XLSX reader - [#734](https://github.com/PHPOffice/PhpSpreadsheet/pull/734)
 - Support overriding `DefaultValueBinder::dataTypeForValue()` without overriding `DefaultValueBinder::bindValue()` - [#735](https://github.com/PHPOffice/PhpSpreadsheet/pull/735)
 - Mpdf export can exceed pcre.backtrack_limit - [#637](https://github.com/PHPOffice/PhpSpreadsheet/issues/637)
+- Fix index overflow on data values array - [#748](https://github.com/PHPOffice/PhpSpreadsheet/pull/748)
 
 ## [1.5.0] - 2018-10-21
 
diff --git a/src/PhpSpreadsheet/Chart/DataSeriesValues.php b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
index fda6ccdf..1d660b0a 100644
--- a/src/PhpSpreadsheet/Chart/DataSeriesValues.php
+++ b/src/PhpSpreadsheet/Chart/DataSeriesValues.php
@@ -271,7 +271,7 @@ class DataSeriesValues
     public function isMultiLevelSeries()
     {
         if (count($this->dataValues) > 0) {
-            return is_array($this->dataValues[0]);
+            return is_array(array_values($this->dataValues)[0]);
         }
 
         return null;