diff --git a/lib/expr/expr.h b/lib/expr/expr.h
index 3d7fbd6..d6cfb53 100644
--- a/lib/expr/expr.h
+++ b/lib/expr/expr.h
@@ -36,6 +36,7 @@ extern "C" {
 #include <stddef.h>
 #include <stdio.h>
 #include <vmalloc/vmalloc.h>
+#include <wchar.h>
 
 #define EX_VERSION	20000101L