diff --git a/swh/deposit/api/checks.py b/swh/deposit/api/checks.py
index ce752cb4..de76a2da 100644
--- a/swh/deposit/api/checks.py
+++ b/swh/deposit/api/checks.py
@@ -1,48 +1,47 @@
 # Copyright (C) 2017-2020  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
 
 """Functional Metadata checks:
 
 Mandatory fields:
 - 'author'
 - 'name' or 'title'
 
 """
 
 from typing import Dict, Optional, Tuple
 
 MANDATORY_FIELDS_MISSING = "Mandatory fields are missing"
 
 
 def check_metadata(metadata: Dict) -> Tuple[bool, Optional[Dict]]:
     """Check metadata for mandatory field presence.
 
     Args:
         metadata: Metadata dictionary to check for mandatory fields
 
     Returns:
         tuple (status, error_detail): True, None if metadata are
           ok (False, <detailed-error>) otherwise.
 
     """
     # at least one value per couple below is mandatory
     alternate_fields = {
         ("atom:name", "atom:title", "codemeta:name"): False,
         ("atom:author", "codemeta:author"): False,
     }
 
     for field, value in metadata.items():
         for possible_names in alternate_fields:
-            for possible_name in possible_names:
-                if possible_name in field:
-                    alternate_fields[possible_names] = True
-                    continue
+            if field in possible_names:
+                alternate_fields[possible_names] = True
+                continue
 
     mandatory_result = [" or ".join(k) for k, v in alternate_fields.items() if not v]
 
     if mandatory_result == []:
         return True, None
     detail = [{"summary": MANDATORY_FIELDS_MISSING, "fields": mandatory_result}]
     return False, {"metadata": detail}
diff --git a/swh/deposit/tests/api/test_checks.py b/swh/deposit/tests/api/test_checks.py
index 7aec749b..3536d0d4 100644
--- a/swh/deposit/tests/api/test_checks.py
+++ b/swh/deposit/tests/api/test_checks.py
@@ -1,94 +1,106 @@
 # Copyright (C) 2017-2020  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 pytest
 
 from swh.deposit.api.checks import check_metadata
 
 
 @pytest.mark.parametrize(
     "metadata_ok",
     [
         {
             "atom:url": "something",
             "atom:external_identifier": "something-else",
             "atom:name": "foo",
             "atom:author": "someone",
         },
         {
             "atom:url": "some url",
             "atom:external_identifier": "some id",
             "atom:title": "bar",
             "atom:author": "no one",
         },
         {"atom:url": "some url", "codemeta:name": "bar", "codemeta:author": "no one",},
     ],
 )
 def test_api_checks_check_metadata_ok(metadata_ok, swh_checks_deposit):
     actual_check, detail = check_metadata(metadata_ok)
     assert actual_check is True, detail
     assert detail is None
 
 
 @pytest.mark.parametrize(
     "metadata_ko,expected_summary",
     [
         (
             {
                 "atom:url": "something",
                 "atom:external_identifier": "something-else",
                 "atom:author": "someone",
             },
             {
                 "summary": "Mandatory fields are missing",
                 "fields": ["atom:name or atom:title or codemeta:name"],
             },
         ),
         (
             {
                 "atom:url": "something",
                 "atom:external_identifier": "something-else",
                 "atom:title": "foobar",
             },
             {
                 "summary": "Mandatory fields are missing",
                 "fields": ["atom:author or codemeta:author"],
             },
         ),
         (
             {
                 "atom:url": "something",
                 "atom:external_identifier": "something-else",
                 "codemeta:title": "bar",
                 "atom:author": "someone",
             },
             {
                 "summary": "Mandatory fields are missing",
                 "fields": ["atom:name or atom:title or codemeta:name"],
             },
         ),
         (
             {
                 "atom:url": "something",
                 "atom:external_identifier": "something-else",
                 "atom:title": "foobar",
                 "author": "foo",
             },
             {
                 "summary": "Mandatory fields are missing",
                 "fields": ["atom:author or codemeta:author"],
             },
         ),
+        (
+            {
+                "atom:url": "something",
+                "atom:external_identifier": "something-else",
+                "atom:title": "foobar",
+                "atom:authorblahblah": "foo",
+            },
+            {
+                "summary": "Mandatory fields are missing",
+                "fields": ["atom:author or codemeta:author"],
+            },
+        ),
     ],
 )
 def test_api_checks_check_metadata_ko(
     metadata_ko, expected_summary, swh_checks_deposit
 ):
     """Missing optional field should be caught
 
     """
     actual_check, error_detail = check_metadata(metadata_ko)
     assert actual_check is False
     assert error_detail == {"metadata": [expected_summary]}