diff --git a/drivers/acpi/acpica/acglobal.h b/drivers/acpi/acpica/acglobal.h
index f3e87ba..f431b99 100644
--- a/drivers/acpi/acpica/acglobal.h
+++ b/drivers/acpi/acpica/acglobal.h
@@ -165,6 +165,10 @@
 ACPI_EXTERN u8 acpi_gbl_integer_byte_width;
 ACPI_EXTERN u8 acpi_gbl_integer_nybble_width;
 
+/* Reader/Writer lock is used for namespace walk and dynamic table unload */
+
+ACPI_EXTERN struct acpi_rw_lock acpi_gbl_namespace_rw_lock;
+
 /*****************************************************************************
  *
  * Mutual exlusion within ACPICA subsystem