diff --git a/sys/conf/dtb.build.mk b/sys/conf/dtb.build.mk
index 9cffe3283906..33a6413e0521 100644
--- a/sys/conf/dtb.build.mk
+++ b/sys/conf/dtb.build.mk
@@ -43,7 +43,7 @@ DTBO=${DTSO:T:R:S/$/.dtbo/}
 
 # Add dependencies on the source file so that out-of-tree things can be included
 # without any .PATH additions.
-.for _dts in ${DTS}
+.for _dts in ${DTS} ${FDT_DTS_FILE}
 ${_dts:R:T}.dtb: ${_dts}
 .endfor
 
diff --git a/sys/conf/kern.post.mk b/sys/conf/kern.post.mk
index a831e94e2415..c25abdd3a7d2 100644
--- a/sys/conf/kern.post.mk
+++ b/sys/conf/kern.post.mk
@@ -8,10 +8,7 @@
 # should be defined in the kern.pre.mk so that port makefiles can
 # override or augment them.
 
-.if !empty(FDT_DTS_FILE)
-DTS+=			${FDT_DTS_FILE}
-.endif
-.if defined(DTS) || defined(DTSO)
+.if defined(DTS) || defined(DTSO) || defined(FDT_DTS_FILE)
 .include "dtb.build.mk"
 
 KERNEL_EXTRA+=	${DTB} ${DTBO}