#include <unistd.h> is neded for the getopt function.

diff --git a/nbtscan.c b/nbtscan.c
index 022627974248785c..fe2290736ba0fc2c 100644
--- a/nbtscan.c
+++ b/nbtscan.c
@@ -8,6 +8,9 @@
 #if HAVE_STDINT_H
 #include <stdint.h>
 #endif
+#if HAVE_UNISTD_H
+#include <unistd.h>
+#endif
 #include "statusq.h"
 #include "range.h"
 #include "list.h"