diff --git a/gtk2_ardour/generic_pluginui.cc b/gtk2_ardour/generic_pluginui.cc
index bc5403099e..5854e5d74b 100644
--- a/gtk2_ardour/generic_pluginui.cc
+++ b/gtk2_ardour/generic_pluginui.cc
@@ -459,9 +459,11 @@ GenericPluginUI::automation_state_changed (ControlUI* cui)
 }
 
 
-static void integer_printer (char buf[32], Adjustment &adj, void */*arg*/)
+static bool
+integer_printer (char buf[32], Adjustment &adj)
 {
 	snprintf (buf, 32, "%.0f", adj.get_value());
+	return true;
 }
 
 void
@@ -574,7 +576,7 @@ GenericPluginUI::build_control_ui (guint32 port_index, boost::shared_ptr<Automat
 		if (desc.integer_step) {
 			control_ui->clickbox = new ClickBox (adj, "PluginUIClickBox");
 			Gtkmm2ext::set_size_request_to_display_given_text (*control_ui->clickbox, "g9999999", 2, 2);
-			control_ui->clickbox->set_print_func (integer_printer, 0);
+			control_ui->clickbox->set_printer (sigc::ptr_fun (integer_printer));
 		} else {
 			//sigc::slot<void,char*,uint32_t> pslot = sigc::bind (sigc::mem_fun(*this, &GenericPluginUI::print_parameter), (uint32_t) port_index);
 
diff --git a/libs/gtkmm2ext/click_box.cc b/libs/gtkmm2ext/click_box.cc
index dc9eb39433..63ab3db7ba 100644
--- a/libs/gtkmm2ext/click_box.cc
+++ b/libs/gtkmm2ext/click_box.cc
@@ -32,8 +32,6 @@ using namespace sigc;
 ClickBox::ClickBox (Gtk::Adjustment *adjp, const string &name, bool round_to_steps)
 	: AutoSpin (*adjp,0,round_to_steps)
 {
-	print_func = default_printer;
-	print_arg = 0;
 	layout = create_pango_layout ("");
 	twidth = 0;
 	theight = 0;
@@ -79,23 +77,16 @@ ClickBox::button_release_handler (GdkEventButton* ev)
 	return true;
 }
 
-void
-ClickBox::default_printer (char buf[32], Gtk::Adjustment &adj, 
-			       void *)
-{
-	sprintf (buf, "%.2f", adj.get_value());
-}
-
 void
 ClickBox::set_label ()
 {
-	if (!print_func) {
-		return;
-	}
-
 	char buf[32];
 
-	print_func (buf, get_adjustment(), print_arg);
+	bool const h = _printer (buf, get_adjustment());
+	if (!h) {
+		/* the printer didn't handle it, so use a default */
+		sprintf (buf, "%.2f", get_adjustment().get_value ());
+	}
 
 	layout->set_text (buf);
 	layout->get_pixel_size (twidth, theight);
@@ -122,31 +113,36 @@ ClickBox::on_expose_event (GdkEventExpose *ev)
 
 	Gtk::DrawingArea::on_expose_event (ev);
 
-	if (print_func) {
-
-		Glib::RefPtr<Gtk::Style> style (get_style());
-		Glib::RefPtr<Gdk::GC> fg_gc (style->get_fg_gc (Gtk::STATE_NORMAL));
-		Glib::RefPtr<Gdk::GC> bg_gc (style->get_bg_gc (Gtk::STATE_NORMAL));
-		Glib::RefPtr<Gdk::Window> win (get_window());
-		
-		GdkRectangle base_rect;
-		GdkRectangle draw_rect;
-		gint x, y, width, height, depth;
-		
-		win->get_geometry (x, y, width, height, depth);
-		
-		base_rect.width = width;
-		base_rect.height = height;
-		base_rect.x = 0;
-		base_rect.y = 0;
-		
-		gdk_rectangle_intersect (&ev->area, &base_rect, &draw_rect);
-		win->draw_rectangle (bg_gc, true, draw_rect.x, draw_rect.y, draw_rect.width, draw_rect.height);
-
-		if (twidth && theight) {
-		  win->draw_layout (fg_gc, (width - twidth) / 2, (height - theight) / 2, layout);
-		}
+	Glib::RefPtr<Gtk::Style> style (get_style());
+	Glib::RefPtr<Gdk::GC> fg_gc (style->get_fg_gc (Gtk::STATE_NORMAL));
+	Glib::RefPtr<Gdk::GC> bg_gc (style->get_bg_gc (Gtk::STATE_NORMAL));
+	Glib::RefPtr<Gdk::Window> win (get_window());
+	
+	GdkRectangle base_rect;
+	GdkRectangle draw_rect;
+	gint x, y, width, height, depth;
+	
+	win->get_geometry (x, y, width, height, depth);
+	
+	base_rect.width = width;
+	base_rect.height = height;
+	base_rect.x = 0;
+	base_rect.y = 0;
+	
+	gdk_rectangle_intersect (&ev->area, &base_rect, &draw_rect);
+	win->draw_rectangle (bg_gc, true, draw_rect.x, draw_rect.y, draw_rect.width, draw_rect.height);
+	
+	if (twidth && theight) {
+		win->draw_layout (fg_gc, (width - twidth) / 2, (height - theight) / 2, layout);
 	}
 
 	return true;
 }
+
+void
+ClickBox::set_printer (sigc::slot<bool, char *, Gtk::Adjustment &> p)
+{
+	_printer = p;
+	set_label ();
+}
+
diff --git a/libs/gtkmm2ext/gtkmm2ext/click_box.h b/libs/gtkmm2ext/gtkmm2ext/click_box.h
index 8f9fb55717..8f9655e2bf 100644
--- a/libs/gtkmm2ext/gtkmm2ext/click_box.h
+++ b/libs/gtkmm2ext/gtkmm2ext/click_box.h
@@ -33,21 +33,17 @@ class ClickBox : public Gtk::DrawingArea, public AutoSpin
 	ClickBox (Gtk::Adjustment *adj, const std::string &name, bool round_to_steps = false);
 	~ClickBox ();
 
-	void set_print_func(void (*pf)(char buf[32], Gtk::Adjustment &, void *),
-			    void *arg) {
-		print_func = pf;
-		print_arg = arg;
-		set_label ();
-	}
-
+	/** Set a slot to `print' the value to put in the box.
+	 *  The slot should write the value of the Gtk::Adjustment
+	 *  into the char array, and should return true if it has done the printing,
+	 *  or false to use the ClickBox's default printing method.
+	 */
+	void set_printer (sigc::slot<bool, char *, Gtk::Adjustment &>);
 
   protected:
 	bool on_expose_event (GdkEventExpose*);
 
   private:
-	void (*print_func) (char buf[32], Gtk::Adjustment &, void *);
-	void *print_arg;
-
 	Glib::RefPtr<Pango::Layout> layout;
 	int twidth;
 	int theight;
@@ -57,7 +53,7 @@ class ClickBox : public Gtk::DrawingArea, public AutoSpin
 	bool button_press_handler (GdkEventButton *);
 	bool button_release_handler (GdkEventButton *);
 
-	static void default_printer (char buf[32], Gtk::Adjustment &, void *);
+	sigc::slot<bool, char *, Gtk::Adjustment &> _printer;
 };
 
 } /* namespace */