diff --git a/Makefile.inc1 b/Makefile.inc1
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -1051,7 +1051,7 @@
 METALOG_SORT_CMD=	env -i LC_COLLATE=C sort
 
 # kernel stage
-KMAKEENV=	${WMAKEENV:NSYSROOT=*}
+KMAKEENV=	${WMAKEENV}
 KMAKE=		${TIME_ENV} ${KMAKEENV} ${MAKE} ${.MAKEFLAGS} ${KERNEL_FLAGS} KERNEL=${INSTKERNNAME}
 
 #
diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -366,6 +366,19 @@
 _ILINKS+= i386
 .endif
 
+.if ${MK_REPRODUCIBLE_BUILD} != "no"
+PREFIX_SYSDIR=/usr/src/sys
+PREFIX_OBJDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/${KERN_IDENT}
+CFLAGS+= -ffile-prefix-map=${SYSDIR}=${PREFIX_SYSDIR}
+CFLAGS+= -ffile-prefix-map=${.OBJDIR}=${PREFIX_OBJDIR}
+.if defined(SYSROOT)
+CFLAGS+= -ffile-prefix-map=${SYSROOT}=/sysroot
+.endif
+.else
+PREFIX_SYSDIR=${SYSDIR}
+PREFIX_OBJDIR=${.OBJDIR}
+.endif
+
 # Ensure that the link exists without depending on it when it exists.
 # Ensure that debug info references the path in the source tree.
 .for _link in ${_ILINKS}
@@ -373,9 +386,9 @@
 ${SRCS} ${DEPENDOBJS}: ${_link}
 .endif
 .if ${_link} == "machine"
-CFLAGS+= -fdebug-prefix-map=./machine=${SYSDIR}/${MACHINE}/include
+CFLAGS+= -fdebug-prefix-map=./machine=${PREFIX_SYSDIR}/${MACHINE}/include
 .else
-CFLAGS+= -fdebug-prefix-map=./${_link}=${SYSDIR}/${_link}/include
+CFLAGS+= -fdebug-prefix-map=./${_link}=${PREFIX_SYSDIR}/${_link}/include
 .endif
 .endfor
 
diff --git a/sys/conf/kmod.mk b/sys/conf/kmod.mk
--- a/sys/conf/kmod.mk
+++ b/sys/conf/kmod.mk
@@ -303,6 +303,25 @@
 beforedepend: ${_ILINKS}
 beforebuild: ${_ILINKS}
 
+.if ${MK_REPRODUCIBLE_BUILD} != "no"
+PREFIX_SYSDIR=/usr/src/sys
+CFLAGS+= -ffile-prefix-map=${SYSDIR}=${PREFIX_SYSDIR}
+.if defined(KERNBUILDDIR)
+PREFIX_KERNBUILDDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/${KERNBUILDDIR:T}
+PREFIX_OBJDIR=${PREFIX_KERNBUILDDIR}/modules/usr/src/sys/modules/${.OBJDIR:T}
+CFLAGS+= -ffile-prefix-map=${KERNBUILDDIR}=${PREFIX_KERNBUILDDIR}
+.else
+PREFIX_OBJDIR=/usr/obj/usr/src/${MACHINE}.${MACHINE_CPUARCH}/sys/modules/${.OBJDIR:T}
+.endif
+CFLAGS+= -ffile-prefix-map=${.OBJDIR}=${PREFIX_OBJDIR}
+.if defined(SYSROOT)
+CFLAGS+= -ffile-prefix-map=${SYSROOT}=/sysroot
+.endif
+.else
+PREFIX_SYSDIR=${SYSDIR}
+PREFIX_OBJDIR=${.OBJDIR}
+.endif
+
 # Ensure that the links exist without depending on it when it exists which
 # causes all the modules to be rebuilt when the directory pointed to changes.
 # Ensure that debug info references the path in the source tree.
@@ -311,9 +330,9 @@
 OBJS_DEPEND_GUESS+=	${_link}
 .endif
 .if ${_link} == "machine"
-CFLAGS+= -fdebug-prefix-map=./machine=${SYSDIR}/${MACHINE}/include
+CFLAGS+= -fdebug-prefix-map=./machine=${PREFIX_SYSDIR}/${MACHINE}/include
 .else
-CFLAGS+= -fdebug-prefix-map=./${_link}=${SYSDIR}/${_link}/include
+CFLAGS+= -fdebug-prefix-map=./${_link}=${PREFIX_SYSDIR}/${_link}/include
 .endif
 .endfor