diff --git a/shells/v7sh/files/Makefile b/shells/v7sh/files/Makefile
index f76184d95e5e..fc1cb9c0a566 100644
--- a/shells/v7sh/files/Makefile
+++ b/shells/v7sh/files/Makefile
@@ -15,7 +15,11 @@ SRCS=   args.c blok.c builtin.c cmd.c ctype.c error.c expand.c \
 
 CWARNFLAGS?=	-ansi -Wbad-function-cast
 WARNS?=	6
+.if ${OSREL:R} < 13
 NO_WERROR=1
+.else
+MK_WERROR=no
+.endif
 WFORMAT=0
 
 .include <bsd.prog.mk>