diff --git a/invenio_rdm_records/contrib/imprint/custom_fields.py b/invenio_rdm_records/contrib/imprint/custom_fields.py
index 3d06681a9..43f10c4ea 100644
--- a/invenio_rdm_records/contrib/imprint/custom_fields.py
+++ b/invenio_rdm_records/contrib/imprint/custom_fields.py
@@ -32,7 +32,7 @@ def field(self):
                 "isbn": SanitizedUnicode(
                     validate=is_isbn,
                     error_messages={
-                        "validator_failed": _("Please provide a valid ISBN.")
+                        "validator_failed": [_("Please provide a valid ISBN.")]
                     },
                 ),
                 "pages": SanitizedUnicode(),
diff --git a/invenio_rdm_records/contrib/journal/custom_fields.py b/invenio_rdm_records/contrib/journal/custom_fields.py
index c5a30c871..e3a3ef27d 100644
--- a/invenio_rdm_records/contrib/journal/custom_fields.py
+++ b/invenio_rdm_records/contrib/journal/custom_fields.py
@@ -34,7 +34,7 @@ def field(self):
                 "issn": SanitizedUnicode(
                     validate=is_issn,
                     error_messages={
-                        "validator_failed": _("Please provide a valid ISSN.")
+                        "validator_failed": [_("Please provide a valid ISSN.")]
                     },
                 ),
             }