diff -up gtk+-2.18.3/gtk/gtktoolbutton.c.toolbutton-assert gtk+-2.18.3/gtk/gtktoolbutton.c
--- gtk+-2.18.3/gtk/gtktoolbutton.c.toolbutton-assert	2009-10-16 10:38:56.000000000 -0400
+++ gtk+-2.18.3/gtk/gtktoolbutton.c	2009-10-26 01:12:26.146186990 -0400
@@ -916,11 +916,15 @@ gtk_tool_button_set_label (GtkToolButton
   button->priv->label_text = g_strdup (label);
   button->priv->contents_invalid = TRUE;     
 
-  elided_label = _gtk_toolbar_elide_underscores (label);
-  accessible = gtk_widget_get_accessible (GTK_WIDGET (button->priv->button));
-  atk_object_set_name (accessible, elided_label);
+  if (label)
+    {
+      elided_label = _gtk_toolbar_elide_underscores (label);
+      accessible = gtk_widget_get_accessible (GTK_WIDGET (button->priv->button));
+      atk_object_set_name (accessible, elided_label);
+
+      g_free (elided_label);
+    }
 
-  g_free (elided_label);
   g_free (old_label);
  
   g_object_notify (G_OBJECT (button), "label");