diff --git a/sys/tools/fdt/make_dtb.sh b/sys/tools/fdt/make_dtb.sh
index a7f5a183c17c..b33dc39609cb 100755
--- a/sys/tools/fdt/make_dtb.sh
+++ b/sys/tools/fdt/make_dtb.sh
@@ -16,12 +16,13 @@ if [ -z "${MACHINE}" ]; then
     MACHINE=$(uname -m)
 fi
 
-: ${DTC:=dtc}
-: ${ECHO:=echo}
+: "${DTC:=dtc}"
+: "${ECHO:=echo}"
+: "${CPP:=cpp}"
 
 for d in ${dts}; do
-    dtb=${dtb_path}/`basename $d .dts`.dtb
+    dtb="${dtb_path}/$(basename "$d" .dts).dtb"
     ${ECHO} "converting $d -> $dtb"
-    cpp -P -x assembler-with-cpp -I $S/gnu/dts/include -I $S/dts/${MACHINE} -I $S/gnu/dts/${MACHINE} -I $S/gnu/dts/ -include $d /dev/null | 
-	${DTC} -@ -O dtb -o $dtb -b 0 -p 1024 -i $S/dts/${MACHINE} -i $S/gnu/dts/${MACHINE} -i $S/gnu/dts/
+    ${CPP} -P -x assembler-with-cpp -I "$S/gnu/dts/include" -I "$S/dts/${MACHINE}" -I "$S/gnu/dts/${MACHINE}" -I "$S/gnu/dts/" -include "$d" /dev/null |
+	${DTC} -@ -O dtb -o "$dtb" -b 0 -p 1024 -i "$S/dts/${MACHINE}" -i "$S/gnu/dts/${MACHINE}" -i "$S/gnu/dts/"
 done
diff --git a/sys/tools/fdt/make_dtbo.sh b/sys/tools/fdt/make_dtbo.sh
index eb1ec1ed3180..edc5d7fd8d41 100755
--- a/sys/tools/fdt/make_dtbo.sh
+++ b/sys/tools/fdt/make_dtbo.sh
@@ -16,12 +16,13 @@ if [ -z "${MACHINE}" ]; then
     MACHINE=$(uname -m)
 fi
 
-: ${DTC:=dtc}
-: ${ECHO:=echo}
+: "${DTC:=dtc}"
+: "${ECHO:=echo}"
+: "${CPP:=cpp}"
 
 for d in ${dtso}; do
-    dtb=${dtbo_path}/`basename $d .dtso`.dtbo
+    dtb="${dtbo_path}/$(basename "$d" .dtso).dtbo"
     ${ECHO} "converting $d -> $dtb"
-    cpp -P -x assembler-with-cpp -I $S/gnu/dts/include -I $S/dts/${MACHINE} -I $S/gnu/dts/${MACHINE} -include $d /dev/null | 
-	${DTC} -@ -O dtb -o $dtb -i $S/dts/${MACHINE} -i $S/gnu/dts/${MACHINE}
+    ${CPP} -P -x assembler-with-cpp -I "$S/gnu/dts/include" -I "$S/dts/${MACHINE}" -I "$S/gnu/dts/${MACHINE}" -include "$d" /dev/null |
+	${DTC} -@ -O dtb -o "$dtb" -i "$S/dts/${MACHINE}" -i "$S/gnu/dts/${MACHINE}"
 done