-

diff --git a/os/os-scrollbar.c b/os/os-scrollbar.c
index 8452844..0e4ad9c 100644
--- a/os/os-scrollbar.c
+++ b/os/os-scrollbar.c
@@ -4166,7 +4166,7 @@ patch_scrollbar_class_vtable (GType type)
   if (widget_class->state_changed == pre_hijacked_scrollbar_state_changed)
     widget_class->state_changed = hijacked_scrollbar_state_changed;
 #endif
-  if (widget_class->grab_notify == pre_hijacked_scrollbar_grab_notify)
+  if (widget_class->grab_notify == pre_hijacked_scrollbar_grab_notify && pre_hijacked_scrollbar_grab_notify)
     widget_class->grab_notify = hijacked_scrollbar_grab_notify;
   if (widget_class->hide == pre_hijacked_scrollbar_hide)
     widget_class->hide = hijacked_scrollbar_hide;