diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk
index a162c018d9cf..de6c9989f223 100644
--- a/sys/conf/kern.mk
+++ b/sys/conf/kern.mk
@@ -230,15 +230,15 @@ CFLAGS+=	-mretpoline
 #
 # Initialize stack variables on function entry
 #
-.if ${MK_INIT_ALL_ZERO} == "yes"
-.if ${COMPILER_FEATURES:Minit-all}
+.if defined(MK_INIT_ALL_ZERO) && ${MK_INIT_ALL_ZERO} == "yes"
+.if defined(COMPILER_FEATURES) && ${COMPILER_FEATURES:Minit-all}
 CFLAGS+= -ftrivial-auto-var-init=zero \
     -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang
 .else
 .warning InitAll (zeros) requested but not support by compiler
 .endif
-.elif ${MK_INIT_ALL_PATTERN} == "yes"
-.if ${COMPILER_FEATURES:Minit-all}
+.elif defined(MK_INIT_ALL_PATTERN) && ${MK_INIT_ALL_PATTERN} == "yes"
+.if defined(COMPILER_FEATURES) && ${COMPILER_FEATURES:Minit-all}
 CFLAGS+= -ftrivial-auto-var-init=pattern
 .else
 .warning InitAll (pattern) requested but not support by compiler