Index: os-prober/linux-boot-prober
===================================================================
--- os-prober.orig/linux-boot-prober
+++ os-prober/linux-boot-prober
@@ -67,7 +67,12 @@ if [ "$type" = btrfs ]; then
 	fi
 	if [ -z "$mpoint" ]; then
 		# mount the btrfs root
-		if ! mount -o subvol=$subvol -t btrfs -U $UUID "$tmpmnt" 2>/dev/null; then
+
+		if [ -n "$subvol" ]; then
+			opts="-o subvol=$subvol"
+		fi
+
+		if ! mount $opts -t btrfs -U $UUID "$tmpmnt" 2>/dev/null; then
 			warn "error mounting btrfs subvol=$subvol UUID=$UUID"
 			umount "$tmpmnt/boot" 2>/dev/null
 			umount "$tmpmnt" 2>/dev/null
Index: os-prober/os-probes/common/50mounted-tests
===================================================================
--- os-prober.orig/os-probes/common/50mounted-tests
+++ os-prober/os-probes/common/50mounted-tests
@@ -114,6 +114,47 @@ if [ "$types" != "btrfs" ]; then
 	exit 1
 fi

+probe_subvol ()
+{
+	local subvol=$1
+	local partition=$2
+	local UUID=$3
+	local tmpmnt=$4
+
+	mounted=
+	mpoint="$(grep btrfs /proc/self/mountinfo | grep "$partition " | grep "/$subvol " | cut -d ' ' -f 5)"
+	ret=1
+
+	if [ -n "$subvol" ]; then
+		opts="-o subvol=$subvol"
+	fi
+
+	if [ -n "$mpoint" ]; then
+		if [ "x$mpoint" = "x/" ]; then
+			continue # this is the root for the running system
+  		fi
+		mounted=1
+	else
+		# again, do not mount btrfs ro
+		mount -t btrfs $opts -U "$UUID" "$tmpmnt"
+		mpoint="$tmpmnt"
+	fi
+	test="/usr/lib/os-probes/mounted/90linux-distro"
+	if [ -f "$test" ] && [ -x "$test" ]; then
+		debug "running subtest $test"
+		if "$test" "$partition" "$mpoint" btrfs "UUID=$UUID" "subvol=$subvol"; then
+			debug "os found by subtest $test on subvol $subvol"
+			ret=0
+		fi
+	fi
+	if [ -z "$mounted" ]; then
+		if ! umount "$tmpmnt"; then
+			warn "failed to umount $tmpmnt"
+		fi
+	fi
+	return $ret
+}
+
 # all btrfs processing here.  Handle both unmounted and
 # mounted subvolumes.
 if [ "$types" = btrfs ]; then
@@ -136,45 +177,23 @@ if [ "$types" = btrfs ]; then
             rmdir "$tmpmnt" || true
             exit 1
         fi
-	if [ -z "$subvols" ]; then
-		debug "no subvols found on btrfs volume $UUID"
-		exit 1
-	fi
+
 	found=
-        for subvol in $subvols; do
-		debug "begin btrfs processing for $UUID subvol=$subvol"
-                if [ "$subvol" != "$defaultvol" ]; then
-			if echo "$rosubvols" | grep -q -x "$subvol"; then
-				continue
-			fi
-			if echo "$sssubvols" | grep -q -x "$subvol"; then
-				continue
-			fi
-		fi
-		mounted=
-		mpoint="$(grep btrfs /proc/self/mountinfo | grep "$partition " | grep "/$subvol " | cut -d ' ' -f 5)"
-		if [ -n "$mpoint" ]; then
-			if [ "x$mpoint" = "x/" ]; then
-				continue # this is the root for the running system
-			fi
-			mounted=1
-		else
-			# again, do not mount btrfs ro
-			mount -t btrfs -o subvol="$subvol" -U "$UUID" "$tmpmnt"
-			mpoint="$tmpmnt"
-		fi
-		test="/usr/lib/os-probes/mounted/90linux-distro"
-		if [ -f "$test" ] && [ -x "$test" ]; then
-			debug "running subtest $test"
-			if "$test" "$partition" "$mpoint" btrfs "UUID=$UUID" "subvol=$subvol"; then
-				debug "os found by subtest $test on subvol $subvol"
-				found=1
-			fi
+	# Always probe subvol or root set as default
+	if probe_subvol "$defaultvol" "$partition" "$UUID" "$tmpmnt"; then
+		found=1
+	fi
+
+	# Probe any other OS on subvol
+	for subvol in $subvols; do
+		if echo "$rosubvols" | grep -q -x "$subvol" ||
+		   echo "$sssubvols" | grep -q -x "$subvol" ||
+		   echo "$defaultvol" | grep -q -x "$subvol"; then
+			continue
 		fi
-		if [ -z "$mounted" ]; then
-			if ! umount "$tmpmnt"; then
-			    warn "failed to umount $tmpmnt"
-			fi
+		debug "begin btrfs processing for $UUID subvol=$subvol"
+		if probe_subvol "$subvol" "$partition" "$UUID" "$tmpmnt"; then
+			found=1
 		fi
 	done
 	rmdir "$tmpmnt" || true