diff --git a/src/lib/empthread/ntthread.c b/src/lib/empthread/ntthread.c
index 1bb29453..bc2e9d9c 100644
--- a/src/lib/empthread/ntthread.c
+++ b/src/lib/empthread/ntthread.c
@@ -49,6 +49,7 @@
 #include <errno.h>
 #include <signal.h>
 #include <stdio.h>
+#include <stdarg.h>
 #include <sys/types.h>
 #include <time.h>
 #include <winsock2.h>