1 files changed, 4 insertions, 0 deletions
diff --git a/src/widgets/styles/qmacstyle_mac.mm b/src/widgets/styles/qmacstyle_mac.mm
index 3918b874e6..6f573ab809 100644
--- a/src/widgets/styles/qmacstyle_mac.mm
+++ b/src/widgets/styles/qmacstyle_mac.mm
@@ -879,6 +879,10 @@ static QSize qt_aqua_get_known_size(QStyle::ContentsType ct, const QWidget *widg
             gbi.size = sz == QAquaSizeSmall ? kHIThemeGrowBoxSizeSmall : kHIThemeGrowBoxSizeNormal;
             if (HIThemeGetGrowBoxBounds(&p, &gbi, &r) == noErr) {
                 int width = 0;
+#ifndef QT_NO_MDIAREA
+            if (widg && qobject_cast<QMdiSubWindow *>(widg->parentWidget()))
+                width = r.size.width;
+#endif
                 ret = QSize(width, r.size.height);
             }
         }