diff --git a/src/widgets/widgets/qdockwidget_p.h b/src/widgets/widgets/qdockwidget_p.h
index 6d3d3077298..f930f0bd297 100644
--- a/src/widgets/widgets/qdockwidget_p.h
+++ b/src/widgets/widgets/qdockwidget_p.h
@@ -117,7 +117,7 @@ class Q_WIDGETS_EXPORT QDockWidgetLayout : public QLayout
 {
     Q_OBJECT
 public:
-    QDockWidgetLayout(QWidget *parent = nullptr);
+    explicit QDockWidgetLayout(QWidget *parent = nullptr);
     ~QDockWidgetLayout();
     void addItem(QLayoutItem *item) override;
     QLayoutItem *itemAt(int index) const override;