diff --git a/workers/dockerfilebuild.py b/workers/dockerfilebuild.py
index b9d2a97a7..73c491d36 100644
--- a/workers/dockerfilebuild.py
+++ b/workers/dockerfilebuild.py
@@ -318,6 +318,7 @@ class DockerfileBuildWorker(Worker):
       'application/octet-stream': DockerfileBuildWorker.__prepare_dockerfile,
       'application/x-tar': DockerfileBuildWorker.__prepare_tarball,
       'application/gzip': DockerfileBuildWorker.__prepare_tarball,
+      'application/x-gzip': DockerfileBuildWorker.__prepare_tarball,
     }
 
     self._timeout = Event()