diff --git a/samples/templates/32readwriteScatterChart3.xlsx b/samples/templates/32readwriteScatterChart3.xlsx
index cfd3a3f2d..1aed96ddb 100644
Binary files a/samples/templates/32readwriteScatterChart3.xlsx and b/samples/templates/32readwriteScatterChart3.xlsx differ
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
index 608eadaf0..37a8e36fc 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/StringTable.php
@@ -306,7 +306,7 @@ class StringTable extends WriterPart
                 $objWriter->writeAttribute('val', $value);
                 $alpha = $underlineColor->getAlpha();
                 if (is_numeric($alpha)) {
-                    $objWriter->startElement('a:alpha');
+                    $objWriter->startElement($prefix . 'alpha');
                     $objWriter->writeAttribute('val', ChartColor::alphaToXml((int) $alpha));
                     $objWriter->endElement();
                 }
diff --git a/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php b/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
index 71b92ab6d..4f8bfaddb 100644
--- a/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
+++ b/tests/PhpSpreadsheetTests/Chart/Charts32ScatterTest.php
@@ -262,6 +262,7 @@ class Charts32ScatterTest extends AbstractFunctional
         self::assertNotNull($chartColor);
         self::assertSame('000000', $chartColor->getValue());
         self::assertSame('srgbClr', $chartColor->getType());
+        self::assertSame(50, $chartColor->getAlpha());
 
         $plotArea = $chart->getPlotArea();
         self::assertNotNull($plotArea);