diff --git a/swh/indexer/metadata_dictionary/maven.py b/swh/indexer/metadata_dictionary/maven.py
index d725f5f..f5f6d9b 100644
--- a/swh/indexer/metadata_dictionary/maven.py
+++ b/swh/indexer/metadata_dictionary/maven.py
@@ -1,158 +1,161 @@
-# 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
 
 import os
 import xml.parsers.expat
 
 import xmltodict
 
 from swh.indexer.codemeta import CROSSWALK_TABLE, SCHEMA_URI
 
 from .base import DictMapping, SingleFileMapping
 
 
 class MavenMapping(DictMapping, SingleFileMapping):
     """
     dedicated class for Maven (pom.xml) mapping and translation
     """
 
     name = "maven"
     filename = b"pom.xml"
     mapping = CROSSWALK_TABLE["Java (Maven)"]
     string_fields = ["name", "version", "description", "email"]
 
     def translate(self, content):
         try:
             d = xmltodict.parse(content).get("project") or {}
         except xml.parsers.expat.ExpatError:
             self.log.warning("Error parsing XML from %s", self.log_suffix)
             return None
         except UnicodeDecodeError:
             self.log.warning("Error unidecoding XML from %s", self.log_suffix)
             return None
         except (LookupError, ValueError):
             # 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)
         return self.normalize_translation(metadata)
 
     _default_repository = {"url": "https://repo.maven.apache.org/maven2/"}
 
     def parse_repositories(self, d):
         """https://maven.apache.org/pom.html#Repositories
 
         >>> import xmltodict
         >>> from pprint import pprint
         >>> d = xmltodict.parse('''
         ... <repositories>
         ...   <repository>
         ...     <id>codehausSnapshots</id>
         ...     <name>Codehaus Snapshots</name>
         ...     <url>http://snapshots.maven.codehaus.org/maven2</url>
         ...     <layout>default</layout>
         ...   </repository>
         ... </repositories>
         ... ''')
         >>> MavenMapping().parse_repositories(d)
         """
         repositories = d.get("repositories")
         if not repositories:
             results = [self.parse_repository(d, self._default_repository)]
         elif isinstance(repositories, dict):
             repositories = repositories.get("repository") or []
             if not isinstance(repositories, list):
                 repositories = [repositories]
             results = [self.parse_repository(d, repo) for repo in repositories]
         else:
             results = []
         return [res for res in results if res] or None
 
     def parse_repository(self, d, repo):
         if not isinstance(repo, dict):
             return
         if repo.get("layout", "default") != "default":
             return  # TODO ?
         url = repo.get("url")
         group_id = d.get("groupId")
         artifact_id = d.get("artifactId")
         if (
             isinstance(url, str)
             and isinstance(group_id, str)
             and isinstance(artifact_id, str)
         ):
             repo = os.path.join(url, *group_id.split("."), artifact_id)
             return {"@id": repo}
 
     def normalize_groupId(self, id_):
         """https://maven.apache.org/pom.html#Maven_Coordinates
 
         >>> MavenMapping().normalize_groupId('org.example')
         {'@id': 'org.example'}
         """
         if isinstance(id_, str):
             return {"@id": id_}
 
     def parse_licenses(self, d):
         """https://maven.apache.org/pom.html#Licenses
 
         >>> import xmltodict
         >>> import json
         >>> d = xmltodict.parse('''
         ... <licenses>
         ...   <license>
         ...     <name>Apache License, Version 2.0</name>
         ...     <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
         ...   </license>
         ... </licenses>
         ... ''')
         >>> print(json.dumps(d, indent=4))
         {
             "licenses": {
                 "license": {
                     "name": "Apache License, Version 2.0",
                     "url": "https://www.apache.org/licenses/LICENSE-2.0.txt"
                 }
             }
         }
         >>> MavenMapping().parse_licenses(d)
         [{'@id': 'https://www.apache.org/licenses/LICENSE-2.0.txt'}]
 
         or, if there are more than one license:
 
         >>> import xmltodict
         >>> from pprint import pprint
         >>> d = xmltodict.parse('''
         ... <licenses>
         ...   <license>
         ...     <name>Apache License, Version 2.0</name>
         ...     <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
         ...   </license>
         ...   <license>
         ...     <name>MIT License</name>
         ...     <url>https://opensource.org/licenses/MIT</url>
         ...   </license>
         ... </licenses>
         ... ''')
         >>> pprint(MavenMapping().parse_licenses(d))
         [{'@id': 'https://www.apache.org/licenses/LICENSE-2.0.txt'},
          {'@id': 'https://opensource.org/licenses/MIT'}]
         """
 
         licenses = d.get("licenses")
         if not isinstance(licenses, dict):
             return
         licenses = licenses.get("license")
         if isinstance(licenses, dict):
             licenses = [licenses]
         elif not isinstance(licenses, list):
             return
         return [
             {"@id": license["url"]}
             for license in licenses
             if isinstance(license, dict) and isinstance(license.get("url"), str)
         ] or None