diff --git a/repo2docker/detectors.py b/repo2docker/detectors.py
index 75fcbc14..470aa601 100644
--- a/repo2docker/detectors.py
+++ b/repo2docker/detectors.py
@@ -716,6 +716,8 @@ class DockerBuildPack(BuildPack):
                 tag=image_spec,
                 buildargs={},
                 decode=True,
+                forcerm=True,
+                rm=True
         ):
             yield line