@@ -2,6 +2,7 @@ package devmapper

 import (

 	"encoding/json"

+	"errors"

 	"fmt"

 	"github.com/dotcloud/docker/utils"

 	"io"

@@ -439,11 +440,11 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {

 	hasMetadata := devices.hasImage("metadata")

 	if !doInit && !hasData {

-		return fmt.Error("Looback data file not found")

+		return errors.New("Looback data file not found")

 	}

 	if !doInit && !hasMetadata {

-		return fmt.Error("Looback metadata file not found")

+		return errors.New("Looback metadata file not found")

 	}

 	createdLoopback := !hasData || !hasMetadata