diff --git a/tar.go b/tar.go
index b2ffba8e..ee0c4436 100644
--- a/tar.go
+++ b/tar.go
@@ -146,7 +146,7 @@ func tarFile(tarWriter *tar.Writer, source, dest string) error {
 		}
 
 		if baseDir != "" {
-			header.Name = filepath.Join(baseDir, strings.TrimPrefix(path, source))
+			header.Name = filepath.ToSlash(filepath.Join(baseDir, strings.TrimPrefix(path, source)))
 		}
 
 		if header.Name == dest {