diff --git a/fs/store_test.go b/fs/store_test.go
index 5d7fa0d0d8..ceefc5e133 100644
--- a/fs/store_test.go
+++ b/fs/store_test.go
@@ -1,7 +1,6 @@
 package fs
 
 import (
-	"errors"
 	"fmt"
 	"github.com/dotcloud/docker/fake"
 	"github.com/dotcloud/docker/future"
@@ -261,7 +260,7 @@ func healthCheck(store *Store) error {
 		for _, img := range images {
 			// Check for duplicate IDs per path
 			if _, exists := IDs[img.Id]; exists {
-				return errors.New(fmt.Sprintf("Duplicate ID: %s", img.Id))
+				return fmt.Errorf("Duplicate ID: %s", img.Id)
 			} else {
 				IDs[img.Id] = true
 			}
@@ -274,7 +273,7 @@ func healthCheck(store *Store) error {
 	// Check non-existing parents
 	for parent := range parents {
 		if _, exists := parents[parent]; !exists {
-			return errors.New("Reference to non-registered parent: " + parent)
+			return fmt.Errorf("Reference to non-registered parent: %s", parent)
 		}
 	}
 	return nil
diff --git a/mount_test.go b/mount_test.go
index 98354875ee..f5bd9e09e7 100644
--- a/mount_test.go
+++ b/mount_test.go
@@ -1,6 +1,7 @@
 package docker
 
 import (
+	"fmt"
 	"github.com/dotcloud/docker/fake"
 	"github.com/dotcloud/docker/fs"
 	"io/ioutil"
@@ -9,7 +10,7 @@ import (
 )
 
 // Look for inconsistencies in a store.
-func healthCheck(store *Store) error {
+func healthCheck(store *fs.Store) error {
 	parents := make(map[string]bool)
 	paths, err := store.Paths()
 	if err != nil {
@@ -24,7 +25,7 @@ func healthCheck(store *Store) error {
 		for _, img := range images {
 			// Check for duplicate IDs per path
 			if _, exists := IDs[img.Id]; exists {
-				return errors.New(fmt.Sprintf("Duplicate ID: %s", img.Id))
+				return fmt.Errorf("Duplicate ID: %s", img.Id)
 			} else {
 				IDs[img.Id] = true
 			}
@@ -37,7 +38,7 @@ func healthCheck(store *Store) error {
 	// Check non-existing parents
 	for parent := range parents {
 		if _, exists := parents[parent]; !exists {
-			return errors.New("Reference to non-registered parent: " + parent)
+			return fmt.Errorf("Reference to non-registered parent: %s", parent)
 		}
 	}
 	return nil