diff --git a/c/buf.c b/c/buf.c
index e398572..570251d 100644
--- a/c/buf.c
+++ b/c/buf.c
@@ -4,6 +4,7 @@
 #include <sys/types.h>
 
 #include <inttypes.h>
+#include <stdarg.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>