diff --git a/share/mk/bsd.mkopt.mk b/share/mk/bsd.mkopt.mk
--- a/share/mk/bsd.mkopt.mk
+++ b/share/mk/bsd.mkopt.mk
@@ -59,6 +59,9 @@
 # step towards removing the options entirely.
 #
 .for var in ${__REQUIRED_OPTIONS}
+.if defined(WITHOUT_${var})
+.warning WITHOUT_${var} option ignored: it is no longer supported
+.endif
 MK_${var}:=	yes
 .endfor