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
@@ -36,6 +36,9 @@
 #
 .for var in ${__DEFAULT_YES_OPTIONS}
 .if !defined(MK_${var})
+.if defined(WITH_${var}) && ${WITH_${var}} == "no"
+.warning "Use WITHOUT_${var}=1 insetad of WITH_${var}=no"
+.endif
 .if defined(WITHOUT_${var})			# WITHOUT always wins
 MK_${var}:=	no
 .else
@@ -54,6 +57,9 @@
 #
 .for var in ${__DEFAULT_NO_OPTIONS}
 .if !defined(MK_${var})
+.if defined(WITH_${var}) && ${WITH_${var}} == "no"
+.warning "Use WITHOUT_${var}=1 insetad of WITH_${var}=no"
+.endif
 .if defined(WITH_${var}) && !defined(WITHOUT_${var}) # WITHOUT always wins
 MK_${var}:=	yes
 .else