diff --git a/swh/lister/nixguix/lister.py b/swh/lister/nixguix/lister.py
--- a/swh/lister/nixguix/lister.py
+++ b/swh/lister/nixguix/lister.py
@@ -25,6 +25,7 @@
 from urllib.parse import urlparse
 
 import requests
+from requests.exceptions import InvalidSchema, SSLError
 
 from swh.core.github.utils import GitHubSession
 from swh.core.tarball import MIMETYPE_TO_ARCHIVE_FORMAT
@@ -155,7 +156,7 @@
 
         try:
             response = request.head(url)
-        except requests.exceptions.InvalidSchema:
+        except (InvalidSchema, SSLError):
             raise ArtifactNatureUndetected(
                 f"Cannot determine artifact type from url <{url}>"
             )
diff --git a/swh/lister/nixguix/tests/data/guix-swh_sources.json b/swh/lister/nixguix/tests/data/guix-swh_sources.json
--- a/swh/lister/nixguix/tests/data/guix-swh_sources.json
+++ b/swh/lister/nixguix/tests/data/guix-swh_sources.json
@@ -24,6 +24,11 @@
       "type": "url",
       "urls": [ "unknown://example.org/wrong-scheme-so-skipped.txt" ],
       "integrity": "sha256-wAEswtkl3ulAw3zq4perrGS6Wlww5XXnQYsEAoYT9fI="
+    },
+    {
+      "type": "url",
+      "urls": [ "https://code.9front.org/hg/plan9front" ],
+      "integrity": "sha256-wAEswtkl3ulAw3zq4perrGS6Wlww5XXnQYsEAoYT9fI="
     }
   ],
   "version":"1",
diff --git a/swh/lister/nixguix/tests/test_lister.py b/swh/lister/nixguix/tests/test_lister.py
--- a/swh/lister/nixguix/tests/test_lister.py
+++ b/swh/lister/nixguix/tests/test_lister.py
@@ -235,6 +235,11 @@
         "ftp://ftp.ourproject.org/file-with-no-extension",
         exc=requests.exceptions.InvalidSchema,
     )
+    # Cannot communicate with an expired cert so skip
+    requests_mock.head(
+        "https://code.9front.org/hg/plan9front",
+        exc=requests.exceptions.SSLError,
+    )
 
     listed_result = lister.run()
     # only the origin upstream is listed, every other entries are unsupported or incomplete