diff --git a/builder/fs/fs.go b/builder/fs/fs.go
index 70d43ead..300b3d10 100644
--- a/builder/fs/fs.go
+++ b/builder/fs/fs.go
@@ -10,6 +10,8 @@ var ErrNotExist = fs.ErrNotExist
 
 var WalkDir = fs.WalkDir
 
+var SkipDir = fs.SkipDir
+
 type DirEntry = fs.DirEntry
 
 type File = fs.File
diff --git a/builder/source.go b/builder/source.go
index 63fdb925..3d9b1ad4 100644
--- a/builder/source.go
+++ b/builder/source.go
@@ -2,7 +2,6 @@ package main
 
 import (
 	"io"
-	"path"
 	"time"
 
 	"github.com/macrat/blanktar/builder/fs"
@@ -72,7 +71,10 @@ func WalkSources(f fs.Readable, fn WalkSourcesFunc) error {
 		if err != nil {
 			return err
 		}
-		if !d.IsDir() && path.Base(name)[0] != '.' {
+		if d.IsDir() && d.Name()[0] == '.' {
+			return fs.SkipDir
+		}
+		if !d.IsDir() && d.Name()[0] != '.' {
 			fn(Source{name, f})
 		}
 		return nil