diff --git a/ingestion/parsers.py b/ingestion/parsers.py
index 4b8a011..160e7ba 100644
--- a/ingestion/parsers.py
+++ b/ingestion/parsers.py
@@ -155,8 +155,11 @@ def partial_context_from_creation_line(data: bytes) -> dict[str, str]:
     creation = _creation_date(lines[20])
     start_year = creation.year if creation.month == 12 else creation.year - 1
     start_month = creation.month % 12 + 1
-    start = date(start_year, start_month, 1)
-    end = date(creation.year, creation.month, monthrange(creation.year, creation.month)[1])
+    try:
+        start = date(start_year, start_month, 1)
+        end = date(creation.year, creation.month, monthrange(creation.year, creation.month)[1])
+    except ValueError:
+        raise ParseError('INVALID_CREATION_DATE') from None
     if (end - start).days > 366:
         raise ParseError('INVALID_CREATION_DATE')
     return {'start_date': start.isoformat(), 'end_date': end.isoformat()}
diff --git a/tests/test_guided_import_workflow.py b/tests/test_guided_import_workflow.py
index 1dd960c..63c49ea 100644
--- a/tests/test_guided_import_workflow.py
+++ b/tests/test_guided_import_workflow.py
@@ -254,6 +254,23 @@ def test_partial_missing_context_has_safe_code_and_no_preview(source):
     assert not ImportBatch.objects.exists()
 
 
+def test_partial_context_year_underflow_does_not_interrupt_another_ready_file(source, bank):
+    card = create_account(name="Synthetic boundary card", kind="CREDIT_CARD", actor=ACTOR)
+    data = ("\n" * 20 + "Data de emissão: 20/01/0001\n"
+            + f"05/01{'Synthetic boundary row':43}BR 12,50 0,00\n").encode()
+    exceptional = source(data, "partial.txt")
+    ready = source()
+    results = [prepare(discovered, account) for discovered, account in ((exceptional, card), (ready, bank))]
+    assert results[0].state == "NEEDS_ATTENTION"
+    assert results[0].code == "INVALID_CREATION_DATE"
+    assert results[0].batch_id is None
+    assert results[1].state == "READY"
+    assert commit(results[1]).counts["created"] == 2
+    assert Transaction.objects.count() == SourceRecord.objects.count() == 2
+    assert not ImportBatch.objects.filter(profile="OUROCARD_PARTIAL_V1").exists()
+    assert_no_open_preview()
+
+
 def test_partial_valid_context_resolves_new_year_and_commits(source):
     card = create_account(name="Synthetic partial card", kind="CREDIT_CARD", actor=ACTOR)
     data = ("\n" * 20 + "Data de emissão: 20/01/2026\n"
diff --git a/tests/test_import_parsers.py b/tests/test_import_parsers.py
index c873030..32d33c1 100644
--- a/tests/test_import_parsers.py
+++ b/tests/test_import_parsers.py
@@ -154,6 +154,20 @@ def test_partial_context_resolves_december_rows_to_the_previous_year_after_janua
     assert rows[0].posting_date == '2025-12-31'
 
 
+@pytest.mark.parametrize('creation', ['20/01/0001', '15/11/0001'])
+def test_partial_context_rejects_derived_interval_year_underflow(creation):
+    data = ('\n' * 20 + f'Data de emissão: {creation}\n').encode()
+    with pytest.raises(ParseError, match='^INVALID_CREATION_DATE$'):
+        partial_context_from_creation_line(data)
+
+
+def test_partial_context_accepts_year_one_when_derived_bounds_are_representable():
+    data = ('\n' * 20 + 'Data de emissão: 15/12/0001\n').encode()
+    assert partial_context_from_creation_line(data) == {
+        'start_date': '0001-01-01', 'end_date': '0001-12-31',
+    }
+
+
 @pytest.mark.parametrize('filename,profile,amounts', [
     ('bank.csv', 'BANK_CSV_V1', ['-12.34','100.00']),
     ('full.txt', 'OUROCARD_FULL_V1', ['-12.34','8.11','33.00']),