diff --git a/container/container.go b/container/container.go
index 0e07c37..24b6783 100644
--- a/container/container.go
+++ b/container/container.go
@@ -242,6 +242,7 @@ func (c Container) Build(image string, envs, runs []string) (err error) {
 		if err != nil {
 			return
 		}
+		buf = []byte(cf)
 	}
 
 	if string(buf) == cf && c.Exist() && UseCache {