diff --git a/sys/fs/unionfs/union_subr.c b/sys/fs/unionfs/union_subr.c
index 7aba881e7ae7..dbed54e6298e 100644
--- a/sys/fs/unionfs/union_subr.c
+++ b/sys/fs/unionfs/union_subr.c
@@ -50,6 +50,7 @@
 #include <sys/fcntl.h>
 #include <sys/filedesc.h>
 #include <sys/stat.h>
+#include <sys/resourcevar.h>
 
 #include <security/mac/mac_framework.h>