diff --git a/include/linux/pnp.h b/include/linux/pnp.h
index b9339d8..cd6332b 100644
--- a/include/linux/pnp.h
+++ b/include/linux/pnp.h
@@ -258,6 +258,7 @@
 #else
 #define pnp_device_is_isapnp(dev) 0
 #endif
+extern struct mutex pnp_res_mutex;
 
 #ifdef CONFIG_PNPBIOS
 extern struct pnp_protocol pnpbios_protocol;