diff --git a/src/frontends/qt/GuiPainter.cpp b/src/frontends/qt/GuiPainter.cpp
index 75e9ace9e2..cf9cd7c118 100644
--- a/src/frontends/qt/GuiPainter.cpp
+++ b/src/frontends/qt/GuiPainter.cpp
@@ -57,7 +57,7 @@ GuiPainter::~GuiPainter()
 
 
 void GuiPainter::setQPainterPen(QColor const & col,
-	Painter::line_style ls, int lw)
+	Painter::line_style ls, int lw, Qt::PenJoinStyle js)
 {
 	if (col == current_color_ && ls == current_ls_ && lw == current_lw_)
 		return;
@@ -79,6 +79,8 @@ void GuiPainter::setQPainterPen(QColor const & col,
 
 	pen.setWidth(lw);
 
+	pen.setJoinStyle(js);
+
 	setPen(pen);
 }
 
@@ -210,7 +212,7 @@ void GuiPainter::rectangle(int x, int y, int w, int h,
 	line_style ls,
 	int lw)
 {
-	setQPainterPen(computeColor(col), ls, lw);
+	setQPainterPen(computeColor(col), ls, lw, Qt::MiterJoin);
 	drawRect(x, y, w, h);
 }
 
diff --git a/src/frontends/qt/GuiPainter.h b/src/frontends/qt/GuiPainter.h
index f3b521bcc0..522b83c65f 100644
--- a/src/frontends/qt/GuiPainter.h
+++ b/src/frontends/qt/GuiPainter.h
@@ -185,7 +185,8 @@ private:
 
 	/// set pen parameters
 	void setQPainterPen(QColor const & col,
-		line_style ls = line_solid, int lw = thin_line);
+		line_style ls = line_solid, int lw = thin_line,
+		Qt::PenJoinStyle js = Qt::BevelJoin);
 
 	// Direction for painting text
 	enum Direction { LtR, RtL, Auto };