diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index 94132b5b515f..3acd43f539e3 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -68,6 +68,15 @@ ${KERNEL_KO}: ${FULLKERNEL} ${KERNEL_KO}.symbols
 	    ${FULLKERNEL} ${.TARGET}
 ${KERNEL_KO}.symbols: ${FULLKERNEL}
 	${OBJCOPY} --only-keep-debug ${FULLKERNEL} ${.TARGET}
+.if defined(MFS_IMAGE)
+	@dd if="${MFS_IMAGE}" ibs=8192 of="${KERNEL_KO}"		\
+	   obs=`strings -at d "${KERNEL_KO}" |				\
+	         grep "MFS Filesystem goes here" | awk '{print $$1}'`	\
+	   oseek=1 conv=notrunc 2>/dev/null &&				\
+	 strings ${KERNEL_KO} |						\
+	 grep 'MFS Filesystem had better STOP here' > /dev/null ||	\
+	 (rm ${KERNEL_KO} && echo 'MFS image too large' && false)
+.endif
 install.debug reinstall.debug: gdbinit
 	cd ${.CURDIR}; ${MAKE} ${.TARGET:R}