diff --git a/tools/rdbgui/rdbgui.ml b/tools/rdbgui/rdbgui.ml
index 69a86a6b96ad5e1978b509add3e406ab3548c1a4..c5bc31fe9f152a423dcbeeec8eb4b244cb78c3f5 100644
--- a/tools/rdbgui/rdbgui.ml
+++ b/tools/rdbgui/rdbgui.ml
@@ -229,14 +229,14 @@ let gui str =
     let par_os_button = GButton.radio_button ~packing:gbox2#add 
         ~group:dot_button#group ~label:"osage*" ()
     in
-    par_dot_button#misc#set_tooltip_text "Use dot, but show only links to parents";
-    par_fd_button#misc#set_tooltip_text "Use fdp, but show only links to parents";
-    par_sf_button#misc#set_tooltip_text "Use sfdp, but show only links to parents";
-    par_ne_button#misc#set_tooltip_text "Use neato, but show only links to parents";
-    par_tw_button#misc#set_tooltip_text "Use twopi, but show only links to parents";
-    par_ci_button#misc#set_tooltip_text "Use circo, but show only links to parents";
-    par_pa_button#misc#set_tooltip_text "Use patchwork, but show only links to parents";
-    par_os_button#misc#set_tooltip_text "Use osage, but show only links to parents";
+    par_dot_button#misc#set_tooltip_text "Use dot, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_fd_button#misc#set_tooltip_text "Use fdp, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_sf_button#misc#set_tooltip_text "Use sfdp, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_ne_button#misc#set_tooltip_text "Use neato, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_tw_button#misc#set_tooltip_text "Use twopi, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_ci_button#misc#set_tooltip_text "Use circo, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_pa_button#misc#set_tooltip_text "Use patchwork, but show only links to the parent (works if State.t contains a 'par:int' field)";
+    par_os_button#misc#set_tooltip_text "Use osage, but show only links to the parent (works if State.t contains a 'par:int' field)";
     ignore (par_dot_button#connect#clicked
               ~callback:(fun () -> p "dot_view := d_par; !dot_view();;"));
     ignore (par_fd_button#connect#clicked