diff --git a/linux/aux-tools/prepare-volatile-img.sh b/linux/aux-tools/prepare-volatile-img.sh
index a31c92e4..33dfc9b9 100755
--- a/linux/aux-tools/prepare-volatile-img.sh
+++ b/linux/aux-tools/prepare-volatile-img.sh
@@ -31,20 +31,23 @@ sfdisk --no-reread -u M "$FILENAME" > /dev/null 2> /dev/null <<EOF
 ,${ROOT_SIZE},L
 EOF
 
-loopdev=`losetup -f --show --partscan "$FILENAME"`
-udevadm settle
-created=
-if [ ! -e ${loopdev}p1 ]; then
-	# device wasn't created automatically, probably udev isn't running;
-	# create devs manually
-	for partdev in /sys/block/$(basename ${loopdev})/loop*p*; do
-		mknod /dev/$(basename ${partdev}) b $(cat ${partdev}/dev | tr : ' ')
-	done
-	created=yes
-fi
-mkswap -f ${loopdev}p1 > /dev/null
-if [ "$created" = "yes" ]; then
-	rm -f ${loopdev}p*
-fi
-losetup -d ${loopdev} || :
-chown --reference `dirname "$FILENAME"` "$FILENAME"
+(
+	flock 200
+	loopdev=`losetup -f --show --partscan "$FILENAME"`
+	udevadm settle
+	created=
+	if [ ! -e ${loopdev}p1 ]; then
+		# device wasn't created automatically, probably udev isn't running;
+		# create devs manually
+		for partdev in /sys/block/$(basename ${loopdev})/loop*p*; do
+			mknod /dev/$(basename ${partdev}) b $(cat ${partdev}/dev | tr : ' ')
+		done
+		created=yes
+	fi
+	mkswap -f ${loopdev}p1 > /dev/null
+	if [ "$created" = "yes" ]; then
+		rm -f ${loopdev}p*
+	fi
+	losetup -d ${loopdev} || :
+	chown --reference `dirname "$FILENAME"` "$FILENAME"
+) 200>"/var/run/qubes/prepare-volatile-img.lock"