diff --git a/src/widgets/widgets/qdockwidget_p.h b/src/widgets/widgets/qdockwidget_p.h
index c1fe3601d17..15544280669 100644
--- a/src/widgets/widgets/qdockwidget_p.h
+++ b/src/widgets/widgets/qdockwidget_p.h
@@ -123,7 +123,7 @@ 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;