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
@@ -42,6 +42,12 @@
 # always += this variable.
 #
 
+__ALL_OPTIONS:= \
+	${__DEFAULT_NO_OPTIONS} \
+	${__DEFAULT_YES_OPTIONS} \
+	${__REQUIRED_OPTIONS} \
+	${__DEFAULT_DEPENDENT_OPTIONS:H}
+
 #
 # MK_* options which default to "yes".
 #
@@ -144,3 +150,19 @@
 MK_${vv:H}:= ${MK_${vv:H}}
 .endfor
 .undef __DEFAULT_DEPENDENT_OPTIONS
+
+#
+# Define SRC_OPT_DEFS and SRC_OPT_LIST
+#
+SRC_OPT_DEFS?=-D__${MACHINE_ARCH}__
+SRC_OPT_LIST?=TARGET=${MACHINE} TARGET_ARCH=${MACHINE_ARCH}
+.for option in ${__ALL_OPTIONS}
+.if ${MK_${option}} == yes
+SRC_OPT_DEFS+=-D${option}
+SRC_OPT_LIST+=WITH_${option}=1
+.else
+SRC_OPT_DEFS+=-U${option}
+SRC_OPT_LIST+=WITHOUT_${option}=1
+.endif
+.endfor
+.undef __ALL_OPTIONS
diff --git a/share/mk/src.opts.mk b/share/mk/src.opts.mk
--- a/share/mk/src.opts.mk
+++ b/share/mk/src.opts.mk
@@ -296,9 +296,9 @@
 .include <bsd.compiler.mk>
 
 .if ${__T} == "i386" || ${__T} == "amd64"
-__DEFAULT_NO_OPTIONS += FDT
+__DEFAULT_NO_OPTIONS+= FDT
 .else
-__DEFAULT_YES_OPTIONS += FDT
+__DEFAULT_YES_OPTIONS+= FDT
 .endif
 
 .if ${__T:Marm*} == "" && ${__T:Mriscv64*} == ""
@@ -519,8 +519,4 @@
 .endif
 .endfor
 
-#
-# Set defaults for the MK_*_SUPPORT variables.
-#
-
 .endif #  !target(__<src.opts.mk>__)