diff --git a/isisd/isis_adjacency.h b/isisd/isis_adjacency.h
index a9b1913..99a8bb2 100644
--- a/isisd/isis_adjacency.h
+++ b/isisd/isis_adjacency.h
@@ -105,7 +105,7 @@
 				     struct isis_circuit *circuit);
 void isis_delete_adj (struct isis_adjacency *adj, struct list *adjdb);
 void isis_adj_state_change (struct isis_adjacency *adj,
-			    enum isis_adj_state state, char *reason);
+			    enum isis_adj_state state, const char *reason);
 void isis_adj_print (struct isis_adjacency *adj);
 int isis_adj_expire (struct thread *thread);
 void isis_adj_print_vty (struct isis_adjacency *adj, struct vty *vty);