diff --git a/sys/alpha/conf/Makefile.alpha b/sys/alpha/conf/Makefile.alpha
index dfd267a69063..a008d9872a9e 100644
--- a/sys/alpha/conf/Makefile.alpha
+++ b/sys/alpha/conf/Makefile.alpha
@@ -23,11 +23,13 @@
 KERNEL?=	kernel
 STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 ALPHA=	${S}/alpha
 
 HCC?=${CC}
diff --git a/sys/conf/Makefile.alpha b/sys/conf/Makefile.alpha
index dfd267a69063..a008d9872a9e 100644
--- a/sys/conf/Makefile.alpha
+++ b/sys/conf/Makefile.alpha
@@ -23,11 +23,13 @@
 KERNEL?=	kernel
 STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 ALPHA=	${S}/alpha
 
 HCC?=${CC}
diff --git a/sys/conf/Makefile.i386 b/sys/conf/Makefile.i386
index f6cd81823193..06d6bb8f5b2f 100644
--- a/sys/conf/Makefile.i386
+++ b/sys/conf/Makefile.i386
@@ -24,11 +24,13 @@ KERNEL?=	kernel
 KERNFORMAT?=	elf
 STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 I386=	${S}/i386
 
 COPTFLAGS?=-O
diff --git a/sys/conf/Makefile.pc98 b/sys/conf/Makefile.pc98
index 7bb71648a6c8..d2b3351e8d76 100644
--- a/sys/conf/Makefile.pc98
+++ b/sys/conf/Makefile.pc98
@@ -26,11 +26,13 @@ KERNEL?=	kernel
 KERNFORMAT?=	elf
 #STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 PC98=	${S}/pc98
 I386=	${S}/i386
 
diff --git a/sys/conf/Makefile.powerpc b/sys/conf/Makefile.powerpc
index f6cd81823193..06d6bb8f5b2f 100644
--- a/sys/conf/Makefile.powerpc
+++ b/sys/conf/Makefile.powerpc
@@ -24,11 +24,13 @@ KERNEL?=	kernel
 KERNFORMAT?=	elf
 STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 I386=	${S}/i386
 
 COPTFLAGS?=-O
diff --git a/sys/i386/conf/Makefile.i386 b/sys/i386/conf/Makefile.i386
index f6cd81823193..06d6bb8f5b2f 100644
--- a/sys/i386/conf/Makefile.i386
+++ b/sys/i386/conf/Makefile.i386
@@ -24,11 +24,13 @@ KERNEL?=	kernel
 KERNFORMAT?=	elf
 STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 I386=	${S}/i386
 
 COPTFLAGS?=-O
diff --git a/sys/pc98/conf/Makefile.pc98 b/sys/pc98/conf/Makefile.pc98
index 7bb71648a6c8..d2b3351e8d76 100644
--- a/sys/pc98/conf/Makefile.pc98
+++ b/sys/pc98/conf/Makefile.pc98
@@ -26,11 +26,13 @@ KERNEL?=	kernel
 KERNFORMAT?=	elf
 #STD8X16FONT?=	iso
 
+.if !defined(S)
 .if exists(./@/.)
 S=	./@
 .else
 S=	../..
 .endif
+.endif
 PC98=	${S}/pc98
 I386=	${S}/i386