diff --git a/libs/gtkmm2ext/gtk_ui.cc b/libs/gtkmm2ext/gtk_ui.cc
index f8a1dc8dbe..d3335e3476 100644
--- a/libs/gtkmm2ext/gtk_ui.cc
+++ b/libs/gtkmm2ext/gtk_ui.cc
@@ -517,6 +517,7 @@ UI::do_request (UIRequest* req)
 			 ) {
 			gtk_widget_set_tooltip_markup (req->widget->gobj(), req->msg);
 		}
+		g_free (old);
 
 	} else {