diff --git a/auth1.c b/auth1.c
index 34dcf62..b9d6b11 100644
--- a/auth1.c
+++ b/auth1.c
@@ -14,6 +14,7 @@
 
 #include <sys/types.h>
 
+#include <stdarg.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>