diff --git a/api.go b/api.go
index 7b82135ef6..ca65c8e119 100644
--- a/api.go
+++ b/api.go
@@ -643,7 +643,7 @@ func postBuild(srv *Server, version float64, w http.ResponseWriter, r *http.Requ
 		}
 	}
 
-	b := NewBuildFile(srv, w)
+	b := NewBuildFile(srv, utils.NewWriteFlusher(w))
 	if _, err := b.Build(file, context); err != nil {
 		return err
 	}