diff --git a/swh/indexer/metadata_dictionary/maven.py b/swh/indexer/metadata_dictionary/maven.py
--- a/swh/indexer/metadata_dictionary/maven.py
+++ b/swh/indexer/metadata_dictionary/maven.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2018-2019  The Software Heritage developers
+# Copyright (C) 2018-2021  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -36,6 +36,9 @@
             # unknown encoding or multi-byte encoding
             self.log.warning("Error detecting XML encoding from %s", self.log_suffix)
             return None
+        if not isinstance(d, dict):
+            self.log.warning("Skipping ill-formed XML content: %s", content)
+            return None
         metadata = self._translate_dict(d, normalize=False)
         metadata[SCHEMA_URI + "codeRepository"] = self.parse_repositories(d)
         metadata[SCHEMA_URI + "license"] = self.parse_licenses(d)