diff --git a/isisd/isis_events.h b/isisd/isis_events.h
index c4bd8ab..86bf051 100644
--- a/isisd/isis_events.h
+++ b/isisd/isis_events.h
@@ -49,7 +49,7 @@
 #define AUTH_ERROR_TYPE_LSP   3
 #define AUTH_ERROR_TYPE_SNP   2
 #define AUTH_ERROR_TYPE_HELLO 1
-void isis_event_auth_failure (char *area_tag, char *error_string,
+void isis_event_auth_failure (char *area_tag, const char *error_string,
 			      u_char *sysid);
 
 #endif /* _ZEBRA_ISIS_EVENTS_H */