diff --git a/aufs/aufs_test.go b/aufs/aufs_test.go
index e4250d9e7b..872f14441b 100644
--- a/aufs/aufs_test.go
+++ b/aufs/aufs_test.go
@@ -426,7 +426,6 @@ func TestChanges(t *testing.T) {
 	}
 }
 
-/* FIXME: How to properly test this?
 func TestDiffSize(t *testing.T) {
 	d := newDriver(t)
 	defer os.RemoveAll(tmp)
@@ -457,7 +456,7 @@ func TestDiffSize(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	diffSize, err := d.DiffSize("1")
+	diffSize, err := d.Size("1")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -465,4 +464,3 @@ func TestDiffSize(t *testing.T) {
 		t.Fatalf("Expected size to be %d got %d", size, diffSize)
 	}
 }
-*/
diff --git a/utils/fs.go b/utils/fs.go
index 891a200507..f07784184c 100644
--- a/utils/fs.go
+++ b/utils/fs.go
@@ -8,6 +8,10 @@ import (
 // TreeSize walks a directory tree and returns its total size in bytes.
 func TreeSize(dir string) (size int64, err error) {
 	err = filepath.Walk(dir, func(d string, fileInfo os.FileInfo, e error) error {
+		// Ignore directory sizes
+		if fileInfo.IsDir() {
+			return nil
+		}
 		size += fileInfo.Size()
 		return nil
 	})