diff --git a/contrib/pg_upgrade/check.c b/contrib/pg_upgrade/check.c
index 50597dba94b..38a8ae0d784 100644
--- a/contrib/pg_upgrade/check.c
+++ b/contrib/pg_upgrade/check.c
@@ -9,6 +9,7 @@
 
 #include "postgres_fe.h"
 
+#include "mb/pg_wchar.h"
 #include "pg_upgrade.h"