diff --git a/core/repair_jobs/acoustid_scanner.py b/core/repair_jobs/acoustid_scanner.py
index e3002430..2f27f741 100644
--- a/core/repair_jobs/acoustid_scanner.py
+++ b/core/repair_jobs/acoustid_scanner.py
@@ -84,14 +84,16 @@ class AcoustIDScannerJob(RepairJob):
             checkpoint_id = context.config_manager.get(
                 f'repair.jobs.{self.job_id}.checkpoint_id', None
             )
+        if checkpoint_id is not None:
+            checkpoint_id = str(checkpoint_id)
 
         # Build ordered list of (track_id, info) sorted by ID for deterministic order
-        track_list = sorted(db_tracks.items(), key=lambda x: x[0])
+        track_list = sorted(db_tracks.items(), key=lambda x: str(x[0]))
 
         # Skip past checkpoint if resuming
         if checkpoint_id is not None:
             original_len = len(track_list)
-            track_list = [(tid, info) for tid, info in track_list if tid > checkpoint_id]
+            track_list = [(tid, info) for tid, info in track_list if str(tid) > checkpoint_id]
             if len(track_list) < original_len:
                 logger.info("Resuming AcoustID scan from checkpoint ID %s (%d tracks remaining)",
                             checkpoint_id, len(track_list))
@@ -258,6 +260,13 @@ class AcoustIDScannerJob(RepairJob):
             """)
             for row in cursor.fetchall():
                 track_id = row[0]
+                if track_id is None:
+                    logger.warning(
+                        "Skipping track row with null ID while loading AcoustID scan candidates: %s",
+                        row[3] or "<unknown file>",
+                    )
+                    continue
+                track_id = str(track_id)
                 tracks[track_id] = {
                     'title': row[1] or '',
                     'artist': row[2] or '',
diff --git a/tests/test_acoustid_scanner.py b/tests/test_acoustid_scanner.py
new file mode 100644
index 00000000..25ebc168
--- /dev/null
+++ b/tests/test_acoustid_scanner.py
@@ -0,0 +1,88 @@
+from types import SimpleNamespace
+
+from core.repair_jobs.acoustid_scanner import AcoustIDScannerJob
+
+
+class _FakeCursor:
+    def __init__(self, rows):
+        self._rows = rows
+        self.executed = []
+
+    def execute(self, query, params=None):
+        self.executed.append((query, params))
+        return self
+
+    def fetchall(self):
+        return self._rows
+
+    def fetchone(self):
+        return None
+
+
+class _FakeConnection:
+    def __init__(self, rows):
+        self._cursor = _FakeCursor(rows)
+
+    def cursor(self):
+        return self._cursor
+
+    def close(self):
+        pass
+
+
+def _make_context(rows):
+    conn = _FakeConnection(rows)
+    config_manager = SimpleNamespace(
+        get=lambda key, default=None: default,
+        set=lambda *args, **kwargs: None,
+    )
+    db = SimpleNamespace(_get_connection=lambda: conn)
+    return SimpleNamespace(
+        db=db,
+        transfer_folder="/music",
+        config_manager=config_manager,
+        acoustid_client=object(),
+        create_finding=None,
+        report_progress=lambda **kwargs: None,
+        update_progress=lambda *args, **kwargs: None,
+        check_stop=lambda: False,
+        wait_if_paused=lambda: False,
+        sleep_or_stop=lambda *args, **kwargs: False,
+    )
+
+
+def test_load_db_tracks_skips_null_ids_and_normalizes_track_ids():
+    job = AcoustIDScannerJob()
+    context = _make_context([
+        (None, "Broken Track", "Artist", "/music/broken.flac", 1, "Album", None, None),
+        (42, "Good Track", "Artist", "/music/good.flac", 2, "Album", "album-thumb", "artist-thumb"),
+    ])
+
+    tracks = job._load_db_tracks(context)
+
+    assert list(tracks.keys()) == ["42"]
+    assert tracks["42"]["title"] == "Good Track"
+    assert tracks["42"]["artist"] == "Artist"
+
+
+def test_scan_handles_mixed_track_id_types(monkeypatch):
+    job = AcoustIDScannerJob()
+    context = _make_context([
+        (None, "Broken Track", "Artist", "/music/broken.flac", 1, "Album", None, None),
+        (42, "Good Track", "Artist", "/music/good.flac", 2, "Album", "album-thumb", "artist-thumb"),
+    ])
+
+    monkeypatch.setattr(job, "_resolve_path", lambda file_path, _context: file_path)
+
+    scanned_track_ids = []
+
+    def fake_scan_file(fpath, track_id, expected, acoustid_client, context, result,
+                       fp_threshold, title_threshold, artist_threshold):
+        scanned_track_ids.append(track_id)
+
+    monkeypatch.setattr(job, "_scan_file", fake_scan_file)
+
+    result = job.scan(context)
+
+    assert result.scanned == 1
+    assert scanned_track_ids == ["42"]