diff --git a/.mailmap b/.mailmap
index 3c2ce6ea..49a287e0 100644
--- a/.mailmap
+++ b/.mailmap
@@ -8,3 +8,5 @@ Odhran O'Donoghue <odhran.r.odonoghue@gmail.com> <39832722+odhran-o-d@users.nore
 Samantha Cox <samc@futurehouse.org> <swrig30@ur.rochester.edu>
 Anush008 <anushshetty90@gmail.com> Anush <anushshetty90@gmail.com>
 Mayk Caldas <mayk@futurehouse.com> maykcaldas <maykcaldas@gmail.com>
+Harry Vu <harry@futurehouse.org> <harryvu-futurehouse@users.noreply.github.com>
+Harry Vu <harry@futurehouse.org> harryvu-futurehouse
diff --git a/paperqa/types.py b/paperqa/types.py
index 5f3f50ff..9d4107ce 100644
--- a/paperqa/types.py
+++ b/paperqa/types.py
@@ -686,6 +686,16 @@ def __add__(self, other: DocDetails | int) -> DocDetails:  # noqa: PLR0912
                 merged_data[field] = {**self.other, **other.other}
                 # handle the bibtex / sources as special fields
                 for field_to_combine in ("bibtex_source", "client_source"):
+                    # Ensure the fields are lists before combining
+                    if self.other.get(field_to_combine) and not isinstance(
+                        self.other[field_to_combine], list
+                    ):
+                        self.other[field_to_combine] = [self.other[field_to_combine]]
+                    if other.other.get(field_to_combine) and not isinstance(
+                        other.other[field_to_combine], list
+                    ):
+                        other.other[field_to_combine] = [other.other[field_to_combine]]
+
                     if self.other.get(field_to_combine) and other.other.get(
                         field_to_combine
                     ):
diff --git a/tests/test_paperqa.py b/tests/test_paperqa.py
index fd5bbba4..690d719a 100644
--- a/tests/test_paperqa.py
+++ b/tests/test_paperqa.py
@@ -6,6 +6,7 @@
 import textwrap
 from collections.abc import AsyncIterable, Sequence
 from copy import deepcopy
+from datetime import datetime, timedelta
 from io import BytesIO
 from pathlib import Path
 from typing import cast
@@ -1239,6 +1240,74 @@ def test_dois_resolve_to_correct_journals(doi_journals):
     assert details.journal == doi_journals["journal"]
 
 
+def test_docdetails_merge_with_non_list_fields() -> None:
+    """Check republication where the source metadata has different shapes."""
+    initial_date = datetime(2023, 1, 1)
+    doc1 = DocDetails(
+        citation="Citation 1",
+        publication_date=initial_date,
+        docname="Document 1",
+        dockey="key1",
+        # NOTE: doc1 has non-list bibtex_source and list client_source
+        other={"bibtex_source": "source1", "client_source": ["client1"]},
+    )
+
+    later_publication_date = initial_date + timedelta(weeks=13)
+    doc2 = DocDetails(
+        citation=doc1.citation,
+        publication_date=later_publication_date,
+        docname=doc1.docname,
+        dockey=doc1.dockey,
+        # NOTE: doc2 has list bibtex_source and non-list client_source
+        other={"bibtex_source": ["source2"], "client_source": "client2"},
+    )
+
+    # Merge the two DocDetails instances
+    merged_doc = doc1 + doc2
+
+    assert {"source1", "source2"}.issubset(
+        merged_doc.other["bibtex_source"]
+    ), "Expected merge to keep both bibtex sources"
+    assert {"client1", "client2"}.issubset(
+        merged_doc.other["client_source"]
+    ), "Expected merge to keep both client sources"
+    assert isinstance(merged_doc, DocDetails), "Merged doc should also be DocDetails"
+
+
+def test_docdetails_merge_with_list_fields() -> None:
+    """Check republication where the source metadata is the same shape."""
+    initial_date = datetime(2023, 1, 1)
+    doc1 = DocDetails(
+        citation="Citation 1",
+        publication_date=initial_date,
+        docname="Document 1",
+        dockey="key1",
+        # NOTE: doc1 has list bibtex_source and list client_source
+        other={"bibtex_source": ["source1"], "client_source": ["client1"]},
+    )
+
+    later_publication_date = initial_date + timedelta(weeks=13)
+    doc2 = DocDetails(
+        citation=doc1.citation,
+        publication_date=later_publication_date,
+        docname=doc1.docname,
+        dockey=doc1.dockey,
+        # NOTE: doc2 has list bibtex_source and list client_source
+        other={"bibtex_source": ["source2"], "client_source": ["client2"]},
+    )
+
+    # Merge the two DocDetails instances
+    merged_doc = doc1 + doc2
+
+    assert {"source1", "source2"}.issubset(
+        merged_doc.other["bibtex_source"]
+    ), "Expected merge to keep both bibtex sources"
+    assert {"client1", "client2"}.issubset(
+        merged_doc.other["client_source"]
+    ), "Expected merge to keep both client sources"
+    assert isinstance(merged_doc, DocDetails), "Merged doc should also be DocDetails"
+
+
 @pytest.mark.vcr
 @pytest.mark.parametrize("use_partition", [True, False])
 @pytest.mark.asyncio