diff --git a/repo2docker/detectors.py b/repo2docker/detectors.py
index 01d53049..ebd15052 100644
--- a/repo2docker/detectors.py
+++ b/repo2docker/detectors.py
@@ -739,6 +739,8 @@ class DockerBuildPack(BuildPack):
                     'JUPYTERHUB_VERSION': self.jupyterhub_version,
                 },
                 decode=True,
+                forcerm=True,
+                rm=True
         ):
             yield line