diff --git a/ospf6d/ospf6_spf.h b/ospf6d/ospf6_spf.h
index 728eec5..c7069c2 100644
--- a/ospf6d/ospf6_spf.h
+++ b/ospf6d/ospf6_spf.h
@@ -77,18 +77,18 @@
 #define VERTEX_IS_TYPE(t, v) \
   ((v)->type == OSPF6_VERTEX_TYPE_ ## t ? 1 : 0)
 
-void ospf6_spf_table_finish (struct ospf6_route_table *result_table);
-void ospf6_spf_calculation (u_int32_t router_id,
-                            struct ospf6_route_table *result_table,
-                            struct ospf6_area *oa);
-void ospf6_spf_schedule (struct ospf6_area *oa);
+extern void ospf6_spf_table_finish (struct ospf6_route_table *result_table);
+extern void ospf6_spf_calculation (u_int32_t router_id,
+                                   struct ospf6_route_table *result_table,
+                                   struct ospf6_area *oa);
+extern void ospf6_spf_schedule (struct ospf6_area *oa);
 
-void ospf6_spf_display_subtree (struct vty *vty, const char *prefix,
-                                int rest, struct ospf6_vertex *v);
+extern void ospf6_spf_display_subtree (struct vty *vty, const char *prefix,
+                                       int rest, struct ospf6_vertex *v);
 
-int config_write_ospf6_debug_spf (struct vty *vty);
-void install_element_ospf6_debug_spf ();
-void ospf6_spf_init ();
+extern int config_write_ospf6_debug_spf (struct vty *vty);
+extern void install_element_ospf6_debug_spf (void);
+extern void ospf6_spf_init (void);
 
 #endif /* OSPF6_SPF_H */