diff --git a/swh/loader/package/nixguix/loader.py b/swh/loader/package/nixguix/loader.py
--- a/swh/loader/package/nixguix/loader.py
+++ b/swh/loader/package/nixguix/loader.py
@@ -214,14 +214,14 @@
                     "Skip source '%s' because key '%s' is missing", source, required_key
                 )
                 valid = False
-        if source["type"] != "url":
+        if valid and source["type"] != "url":
             logger.info(
                 "Skip source '%s' because the type %s is not supported",
                 source,
                 source["type"],
             )
             valid = False
-        if not isinstance(source["urls"], list):
+        if valid and not isinstance(source["urls"], list):
             logger.info(
                 "Skip source '%s' because the urls attribute is not a list", source
             )
diff --git a/swh/loader/package/nixguix/tests/test_nixguix.py b/swh/loader/package/nixguix/tests/test_nixguix.py
--- a/swh/loader/package/nixguix/tests/test_nixguix.py
+++ b/swh/loader/package/nixguix/tests/test_nixguix.py
@@ -83,6 +83,8 @@
             {"type": "url", "urls": "my-url", "integrity": "my-integrity"},
             # type is not url
             {"type": "git", "urls": ["my-url"], "integrity": "my-integrity"},
+            # missing fields which got double-checked nonetheless...
+            {"integrity": "my-integrity"},
         ],
         "revision": "my-revision",
     }