diff --git a/gtk2_ardour/processor_box.cc b/gtk2_ardour/processor_box.cc
index 2e1942f7d3..e40b8e9bf9 100644
--- a/gtk2_ardour/processor_box.cc
+++ b/gtk2_ardour/processor_box.cc
@@ -546,6 +546,7 @@ ProcessorEntry::Control::button_clicked ()
 
 	c->set_value (n ? 0 : 1);
 	_button.set_active (!n);
+	set_tooltip ();
 }
 
 void