diff --git a/src/name_lookup.c b/src/name_lookup.c
index 2b68bb4..77f823d 100644
--- a/src/name_lookup.c
+++ b/src/name_lookup.c
@@ -21,6 +21,7 @@
  */
 
 #include <stdlib.h>
+#include <stdarg.h>
 #include <string.h>
 #include <curl/curl.h>