diff --git a/swh/core/tarball.py b/swh/core/tarball.py
--- a/swh/core/tarball.py
+++ b/swh/core/tarball.py
@@ -19,6 +19,7 @@
     "application/x-tar": "tar",
     "application/x-bzip2": "bztar",
     "application/gzip": "gztar",
+    "application/x-gzip": "gztar",
     "application/x-lzip": "tar.lz",
     "application/zip": "zip",
     "application/java-archive": "jar",