diff --git a/ospf6d/ospf6_interface.h b/ospf6d/ospf6_interface.h
index fb93ced..878c29e 100644
--- a/ospf6d/ospf6_interface.h
+++ b/ospf6d/ospf6_interface.h
@@ -124,29 +124,28 @@
 
 /* Function Prototypes */
 
-struct ospf6_interface *ospf6_interface_lookup_by_ifindex (int);
-struct ospf6_interface *ospf6_interface_create (struct interface *);
-void ospf6_interface_delete (struct ospf6_interface *);
+extern struct ospf6_interface *ospf6_interface_lookup_by_ifindex (int);
+extern struct ospf6_interface *ospf6_interface_create (struct interface *);
+extern void ospf6_interface_delete (struct ospf6_interface *);
 
-void ospf6_interface_enable (struct ospf6_interface *);
-void ospf6_interface_disable (struct ospf6_interface *);
+extern void ospf6_interface_enable (struct ospf6_interface *);
+extern void ospf6_interface_disable (struct ospf6_interface *);
 
-void ospf6_interface_if_add (struct interface *);
-void ospf6_interface_if_del (struct interface *);
-void ospf6_interface_state_update (struct interface *);
-void ospf6_interface_connected_route_update (struct interface *);
+extern void ospf6_interface_if_add (struct interface *);
+extern void ospf6_interface_if_del (struct interface *);
+extern void ospf6_interface_state_update (struct interface *);
+extern void ospf6_interface_connected_route_update (struct interface *);
 
 /* interface event */
-int interface_up (struct thread *);
-int interface_down (struct thread *);
-int wait_timer (struct thread *);
-int backup_seen (struct thread *);
-int neighbor_change (struct thread *);
+extern int interface_up (struct thread *);
+extern int interface_down (struct thread *);
+extern int wait_timer (struct thread *);
+extern int backup_seen (struct thread *);
+extern int neighbor_change (struct thread *);
 
-void ospf6_interface_init ();
+extern void ospf6_interface_init (void);
 
-int config_write_ospf6_debug_interface (struct vty *vty);
-void install_element_ospf6_debug_interface ();
+extern int config_write_ospf6_debug_interface (struct vty *vty);
+extern void install_element_ospf6_debug_interface (void);
 
 #endif /* OSPF6_INTERFACE_H */
-