diff --git a/src/plugins/platforms/cocoa/qcocoacolordialoghelper.mm b/src/plugins/platforms/cocoa/qcocoacolordialoghelper.mm
index bfc626fdbac..fd4d6605a97 100644
--- a/src/plugins/platforms/cocoa/qcocoacolordialoghelper.mm
+++ b/src/plugins/platforms/cocoa/qcocoacolordialoghelper.mm
@@ -404,6 +404,11 @@ void QCocoaColorDialogHelper::setCurrentColor_sys(const QColor &color)
     if (!mDelegate)
         createNSColorPanelDelegate();
     QT_MANGLE_NAMESPACE(QNSColorPanelDelegate) *delegate = static_cast<QT_MANGLE_NAMESPACE(QNSColorPanelDelegate) *>(mDelegate);
+
+    // make sure that if ShowAlphaChannel option is set then also setShowsAlpha
+    // needs to be set, otherwise alpha value is omitted
+    [delegate->mColorPanel setShowsAlpha:options()->testOption(QColorDialogOptions::ShowAlphaChannel)];
+
     NSColor *nsColor;
     const QColor::Spec spec = color.spec();
     if (spec == QColor::Cmyk) {
diff --git a/tests/auto/widgets/dialogs/qcolordialog/tst_qcolordialog.cpp b/tests/auto/widgets/dialogs/qcolordialog/tst_qcolordialog.cpp
index ff34b009e94..e6d3e56a43a 100644
--- a/tests/auto/widgets/dialogs/qcolordialog/tst_qcolordialog.cpp
+++ b/tests/auto/widgets/dialogs/qcolordialog/tst_qcolordialog.cpp
@@ -156,9 +156,6 @@ void tst_QColorDialog::task247349_alpha()
     dialog.setOption(QColorDialog::ShowAlphaChannel, true);
     int alpha = 0x17;
     dialog.setCurrentColor(QColor(0x01, 0x02, 0x03, alpha));
-#ifdef Q_OS_MAC
-    QEXPECT_FAIL("", "Fails on Mac OS X, see QTBUG-24320", Abort);
-#endif
     QCOMPARE(alpha, dialog.currentColor().alpha());
     QCOMPARE(alpha, qAlpha(dialog.currentColor().rgba()));
 }