diff --git a/hxnum.c b/hxnum.c
index c6bc852..729dc67 100644
--- a/hxnum.c
+++ b/hxnum.c
@@ -30,6 +30,7 @@
 #include <stdlib.h>
 #include <err.h>
 #include <sysexits.h>
+#include <getopt.h>
 #include <assert.h>
 #include "export.h"
 #include "types.e"