diff --git a/ospf6d/ospf6_proto.h b/ospf6d/ospf6_proto.h
index 2b6ae54..9fe821d 100644
--- a/ospf6d/ospf6_proto.h
+++ b/ospf6d/ospf6_proto.h
@@ -116,7 +116,7 @@
 void ospf6_prefix_options_printbuf (u_int8_t prefix_options,
                                     char *buf, int size);
 void ospf6_capability_printbuf (char capability, char *buf, int size);
-void ospf6_options_printbuf (char *options, char *buf, int size);
+void ospf6_options_printbuf (u_char *options, char *buf, int size);
 
 #endif /* OSPF6_PROTO_H */