Index: os-prober/linux-boot-prober
===================================================================
--- os-prober.orig/linux-boot-prober
+++ os-prober/linux-boot-prober
@@ -90,15 +90,9 @@ if [ "$type" = btrfs ]; then
 		# /boot is part of the root
 		bootpart="$partition"
 		bootsv="$subvol"
-	elif echo "$bootmnt" | cut -d ' ' -f 3 | grep -q "btrfs"; then
+	elif echo "$bootmnt" | cut -d ' ' -f 3 | grep -q "btrfs" && echo "$bootmnt" | cut -d ' ' -f 4 | grep -q "subvol="; then
 		# separate btrfs /boot subvolume
 		bootsv=$(echo "$bootmnt" | cut -d ' ' -f 4 | sed -n 's!\(^subvol=\|.*,subvol=\)\([^,]\+\).*!\2!p')
-		if [ -z "$bootsv" ]; then
-			warn "no subvolume in entry: $bootmnt"
-			umount "$tmpmnt" 2>/dev/null
-			rmdir "$tmpmnt" 2>/dev/null
-			exit 1
-		fi
 		bootuuid=$(echo "$bootmnt" | cut -d ' ' -f 1 | sed -n 's/UUID=\("\(.*\)"\|\(.*\)\)/\2\3/p')
 		debug "mounting btrfs $tmpmnt/boot UUID=$bootuuid subvol=$bootsv"
 		bindfrom=$(check_btrfs_mounted $bootsv $bootuuid)