diff --git a/libio/fwide.c b/libio/fwide.c
index a4d0e4708c..c749c5242a 100644
--- a/libio/fwide.c
+++ b/libio/fwide.c
@@ -25,6 +25,7 @@
 
 #include <libioP.h>
 #include <stdio.h>
+#include <wchar.h>
 
 int
 fwide (fp, mode)