--- /usr/share/initramfs-tools/scripts/functions.orig	2015-07-08 10:48:26.000000000 +0200
+++ /usr/share/initramfs-tools/scripts/functions	2015-07-08 10:39:15.000000000 +0200
@@ -324,6 +324,10 @@
 	UUID=*)
 		DEV="/dev/disk/by-uuid/${DEV#UUID=}"
 		;;
+	/dev/mapper/*)
+		echo "$DEV"
+		return 0
+		;;
 	esac
 	# Only canonicalise if a valid file, in case $DEV isn't a filename
 	[ -e "$DEV" ] && DEV=$(readlink -f "$DEV")