diff --git a/src/paperless_ai/tests/test_legacy_lance_cleanup.py b/src/paperless_ai/tests/test_legacy_lance_cleanup.py
new file mode 100644
index 000000000..7f0c64ef0
--- /dev/null
+++ b/src/paperless_ai/tests/test_legacy_lance_cleanup.py
@@ -0,0 +1,100 @@
+from pathlib import Path
+
+import pytest
+from django.utils import timezone
+
+from documents.models import Document
+from paperless_ai import indexing
+from paperless_ai.tests.conftest import FakeEmbedding
+
+
+@pytest.fixture
+def legacy_lance_dir(temp_llm_index_dir: Path) -> Path:
+    """Simulate leftovers of a pre-sqlite-vec LanceDB index."""
+    lance_table = temp_llm_index_dir / "documents.lance"
+    (lance_table / "data").mkdir(parents=True)
+    (lance_table / "data" / "0000.lance").write_bytes(b"not a real lance file")
+    (temp_llm_index_dir / "meta.json").write_text("{}")
+    return lance_table
+
+
+@pytest.mark.django_db
+class TestLegacyLanceCleanup:
+    def test_update_removes_legacy_dir_and_forces_rebuild(
+        self,
+        legacy_lance_dir: Path,
+        temp_llm_index_dir: Path,
+        mock_embed_model: FakeEmbedding,
+        caplog: pytest.LogCaptureFixture,
+    ) -> None:
+        """When a LanceDB directory is present, update_llm_index must delete it,
+        log a rebuild warning, and produce a valid (empty) sqlite-vec store."""
+        Document.objects.create(
+            title="Test Document",
+            content="Some content for legacy lance cleanup test.",
+            added=timezone.now(),
+        )
+
+        indexing.update_llm_index(rebuild=False)
+
+        assert not legacy_lance_dir.exists()
+        assert not (temp_llm_index_dir / "meta.json").exists()
+        assert "forcing a full rebuild" in caplog.text
+        store = indexing.get_vector_store()
+        assert store.table_exists()
+
+    def test_update_without_legacy_dir_does_not_force_rebuild(
+        self,
+        temp_llm_index_dir: Path,
+        mock_embed_model: FakeEmbedding,
+        caplog: pytest.LogCaptureFixture,
+    ) -> None:
+        """When no LanceDB leftovers exist, incremental update must not log a
+        forced-rebuild warning on a second call."""
+        Document.objects.create(
+            title="Test Document",
+            content="Some content without legacy lance.",
+            added=timezone.now(),
+        )
+
+        # First call builds the index cleanly (no legacy lance present).
+        indexing.update_llm_index(rebuild=True)
+
+        caplog.clear()
+
+        # Second incremental call must not mention a forced rebuild.
+        indexing.update_llm_index(rebuild=False)
+
+        assert "forcing a full rebuild" not in caplog.text
+
+    def test_cleanup_helper_reports_absence(self, temp_llm_index_dir: Path) -> None:
+        """_cleanup_legacy_lance_index must return False when no lance dir exists."""
+        assert indexing._cleanup_legacy_lance_index() is False  # noqa: SLF001
+
+    def test_cleanup_helper_reports_presence(
+        self,
+        legacy_lance_dir: Path,
+        temp_llm_index_dir: Path,
+    ) -> None:
+        """_cleanup_legacy_lance_index must return True and remove the directory."""
+        result = indexing._cleanup_legacy_lance_index()  # noqa: SLF001
+
+        assert result is True
+        assert not legacy_lance_dir.exists()
+        assert not (temp_llm_index_dir / "meta.json").exists()
+
+    def test_cleanup_helper_removes_only_lance_not_other_files(
+        self,
+        legacy_lance_dir: Path,
+        temp_llm_index_dir: Path,
+    ) -> None:
+        """_cleanup_legacy_lance_index must not touch files other than the lance dir
+        and meta.json."""
+        other_file = temp_llm_index_dir / "index.db"
+        other_file.write_bytes(b"sqlite data")
+
+        indexing._cleanup_legacy_lance_index()  # noqa: SLF001
+
+        assert other_file.exists(), (
+            "unrelated files in LLM_INDEX_DIR must be left intact after cleanup"
+        )