diff --git a/gtk2_ardour/prh.cc b/gtk2_ardour/prh.cc
index 666878a4cf..c896cfd558 100644
--- a/gtk2_ardour/prh.cc
+++ b/gtk2_ardour/prh.cc
@@ -98,10 +98,10 @@ PianoRollHeader::size_request (double& w, double& h) const
 	if (show_scroomer()) {
 		_scroomer_size = 60.f * UIConfiguration::instance().get_ui_scale();
 	} else {
-		_scroomer_size = 20.f * UIConfiguration::instance().get_ui_scale();
+		_scroomer_size = kbd_width * UIConfiguration::instance().get_ui_scale();
 	}
 
-	w = _scroomer_size +  20.;
+	w = _scroomer_size + (kbd_width * UIConfiguration::instance().get_ui_scale());
 }
 
 bool
diff --git a/gtk2_ardour/prh_base.cc b/gtk2_ardour/prh_base.cc
index e801fdca80..2febf02b50 100644
--- a/gtk2_ardour/prh_base.cc
+++ b/gtk2_ardour/prh_base.cc
@@ -241,7 +241,6 @@ PianoRollHeaderBase::render (ArdourCanvas::Rect const & self, ArdourCanvas::Rect
 		origin_y -= 1;
 	}
 
-
 	cr->translate (origin_x, origin_y);
 
 	// Render the MIDNAM text or its equivalent.  First, set up a clip
@@ -351,13 +350,14 @@ PianoRollHeaderBase::render (ArdourCanvas::Rect const & self, ArdourCanvas::Rect
 
 		}
 
-
 		Gtkmm2ext::set_source_rgba (cr, bg);
 
-		double x = _scroomer_size;;
+		assert (_scroomer_size = width() - kbd_width);
+
+		double x = _scroomer_size;
 		double y = positions[n];
 
-		cr->rectangle (x, y, width() - 1., heights[n]);
+		cr->rectangle (x, y, kbd_width, heights[n]);
 		cr->fill ();
 
 		if ((oct_rel == 4 || oct_rel == 11) && y > 0) {
@@ -369,7 +369,7 @@ PianoRollHeaderBase::render (ArdourCanvas::Rect const & self, ArdourCanvas::Rect
 			   which are rects
 			*/
 			cr->move_to (x, y + 0.5);
-			cr->line_to (x + width(), y + 0.5);
+			cr->line_to (x + kbd_width, y + 0.5);
 			cr->stroke ();
 		}
 	}
diff --git a/gtk2_ardour/prh_base.h b/gtk2_ardour/prh_base.h
index a6714819d2..8cc4becba3 100644
--- a/gtk2_ardour/prh_base.h
+++ b/gtk2_ardour/prh_base.h
@@ -103,6 +103,7 @@ class PianoRollHeaderBase : virtual public sigc::trackable {
 	double _saved_bottom_val;
 	mutable bool _mini_map_display;
 	bool entered;
+	static const int kbd_width = 20;
 
 	// void on_size_request(Gtk::Requisition*);