diff --git a/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp b/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
index d69cf11a47a..e83f49ab82b 100644
--- a/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
+++ b/src/plugins/diffeditor/sidebysidediffeditorwidget.cpp
@@ -123,7 +123,7 @@ protected:
     void drawCollapsedBlockPopup(QPainter &painter,
                                  const QTextBlock &block,
                                  QPointF offset,
-                                 const QRect &clip);
+                                 const QRect &clip) override;
 
 private:
     void paintSeparator(QPainter &painter, QColor &color, const QString &text,