diff --git a/src/output.c b/src/output.c
index 7c29d4f..407b2a8 100644
--- a/src/output.c
+++ b/src/output.c
@@ -43,6 +43,7 @@
 #include <errno.h>
 #include <inttypes.h>
 #include <langinfo.h>
+#include <locale.h>
 #include <math.h>
 #include <netinet/in.h>
 #include <stdio.h>