diff --git a/include/scsi/sg.h b/include/scsi/sg.h
index 934ae38..a9f3c6f 100644
--- a/include/scsi/sg.h
+++ b/include/scsi/sg.h
@@ -70,6 +70,9 @@
  (for the lk 2.2 series).
 */
 
+#ifdef __KERNEL__
+extern int sg_big_buff; /* for sysctl */
+#endif
 
 /* New interface introduced in the 3.x SG drivers follows */