diff --git a/include/cxx/cwchar b/include/cxx/cwchar
index fa70b9d53b..2e860b14ea 100644
--- a/include/cxx/cwchar
+++ b/include/cxx/cwchar
@@ -43,6 +43,7 @@
 #include <nuttx/config.h>
 
 #include <wchar.h>
+#include <wctype.h>
 #include <stdlib.h>
 
 //***************************************************************************