diff --git a/multibuild.py b/multibuild.py
index 7442686..1a9b7cb 100644
--- a/multibuild.py
+++ b/multibuild.py
@@ -93,7 +93,7 @@ def find_artifacts(directory="out"):
         return join(directory, _)
 
 
-def get_dockerfile_contents(props):
+def _get_dockerfile_contents(props):
     """
     Read contents of a Dockerfile and add extra contents for the given os_codename
     """
@@ -108,6 +108,11 @@ def get_dockerfile_contents(props):
     }[util.Interpolate("%(prop:os_codename)s")]
 
 
+@util.renderer
+def get_dockerfile_contents(props):
+    return _get_dockerfile_contents(props)
+
+
 def trigger_child_hooks(buildbotUrl: str, os_codename: str, repository, branch, jobname, directory=".buildbot"):
     request_url = buildbotUrl + ty