diff --git a/share/mk/bsd.sys.mk b/share/mk/bsd.sys.mk
index 8446b8eeae6..9d24c87d9ee 100644
--- a/share/mk/bsd.sys.mk
+++ b/share/mk/bsd.sys.mk
@@ -149,7 +149,7 @@ WFORMAT=	1
 .if ${WFORMAT} > 0
 #CWARNFLAGS+=	-Wformat-nonliteral -Wformat-security -Wno-format-extra-args
 CWARNFLAGS+=	-Wformat=2 -Wno-format-extra-args
-.if ${WARNS} <= 3
+.if ${WARNS:U0} <= 3
 CWARNFLAGS.clang+=	-Wno-format-nonliteral
 .endif # WARNS <= 3
 .if ${MK_WERROR} != "no" && ${MK_WERROR.${COMPILER_TYPE}:Uyes} != "no"