diff --git a/core/library/manual_library_match.py b/core/library/manual_library_match.py
index 132ad729..ef14af9f 100644
--- a/core/library/manual_library_match.py
+++ b/core/library/manual_library_match.py
@@ -14,12 +14,27 @@ from utils.logging_config import get_logger
 logger = get_logger("library.manual_library_match")
 
 
+def normalize_library_track_id(value: Any) -> Optional[str]:
+    """Normalize an incoming library_track_id to the opaque string id we store.
+
+    Library track ids are ``str(ratingKey)`` — numeric strings for Plex, but
+    GUIDs/hashes for Jellyfin, Navidrome, and other Subsonic servers (see
+    ``tracks.id`` which is TEXT). They must NOT be coerced to int: doing so
+    rejected every non-numeric id with "Invalid library track id". We only
+    reject empty/None here; the caller validates existence against the DB.
+    """
+    if value is None:
+        return None
+    text = str(value).strip()
+    return text or None
+
+
 def save_match(
     db,
     profile_id: int,
     source: str,
     source_track_id: str,
-    library_track_id: int,
+    library_track_id: str,
     **meta,
 ) -> bool:
     """Save (insert or replace) a manual match."""
diff --git a/database/music_database.py b/database/music_database.py
index 4e443253..2855f4ed 100644
--- a/database/music_database.py
+++ b/database/music_database.py
@@ -4440,7 +4440,7 @@ class MusicDatabase:
             logger.error(f"Error creating manual_library_track_matches table: {e}")
 
     def save_manual_library_match(self, profile_id: int, source: str, source_track_id: str,
-                                   library_track_id: int, **meta) -> bool:
+                                   library_track_id: str, **meta) -> bool:
         """Insert or replace a manual match. meta keys: source_title, source_artist,
         source_album, source_context_json, server_source."""
         try:
diff --git a/tests/test_manual_library_match.py b/tests/test_manual_library_match.py
index 7804eb25..6329a01c 100644
--- a/tests/test_manual_library_match.py
+++ b/tests/test_manual_library_match.py
@@ -16,6 +16,56 @@ def db(tmp_path):
     return MusicDatabase(str(tmp_path / "music.db"))
 
 
+# ---------------------------------------------------------------------------
+# normalize_library_track_id — regression guard for issue #754
+# ("Invalid library track id" on Jellyfin/Navidrome/Subsonic servers)
+# ---------------------------------------------------------------------------
+
+def test_normalize_passes_numeric_plex_id():
+    # Plex ratingKeys are numeric strings — must survive unchanged (not int-ified).
+    assert mlm.normalize_library_track_id("12345") == "12345"
+    assert mlm.normalize_library_track_id(12345) == "12345"
+
+
+def test_normalize_passes_guid_id():
+    # The #754 bug: Jellyfin/Navidrome ids are non-numeric. int() rejected them.
+    assert mlm.normalize_library_track_id("a1b2c3d4-e5f6") == "a1b2c3d4-e5f6"
+    assert mlm.normalize_library_track_id("Do I Wanna Know_opus") == "Do I Wanna Know_opus"
+
+
+def test_normalize_trims_whitespace():
+    assert mlm.normalize_library_track_id("  guid-123  ") == "guid-123"
+
+
+def test_normalize_rejects_empty_and_none():
+    assert mlm.normalize_library_track_id(None) is None
+    assert mlm.normalize_library_track_id("") is None
+    assert mlm.normalize_library_track_id("   ") is None
+
+
+def test_guid_library_track_id_round_trips(db):
+    """End-to-end regression for #754: a non-numeric library id must save,
+    read back identically, and enrich — never get coerced or rejected."""
+    guid = "a1b2c3d4e5f6-jellyfin"
+    norm = mlm.normalize_library_track_id(guid)
+    assert norm == guid
+    ok = db.save_manual_library_match(1, "spotify", "src-track-1", norm,
+                                       source_title="Do I Wanna Know?",
+                                       source_artist="Arctic Monkeys")
+    assert ok is True
+    row = db.get_manual_library_match(1, "spotify", "src-track-1")
+    assert row is not None
+    assert row["library_track_id"] == guid  # stored as-is, not mangled to int
+
+    # Enrichment must resolve the GUID against tracks.id (TEXT) without error.
+    with patch.object(db, "api_get_tracks_by_ids", return_value=[
+            {"title": "Do I Wanna Know?", "artist_name": "Arctic Monkeys",
+             "album_title": "AM", "file_path": "/m/x.opus", "bitrate": 196}]) as mock_get:
+        enriched = mlm._enrich_match(row, db)
+    mock_get.assert_called_once_with([guid])  # passes the string id straight through
+    assert enriched["library_title"] == "Do I Wanna Know?"
+
+
 # ---------------------------------------------------------------------------
 # DB-layer tests
 # ---------------------------------------------------------------------------
diff --git a/web_server.py b/web_server.py
index fd86abb0..51724911 100644
--- a/web_server.py
+++ b/web_server.py
@@ -18608,13 +18608,9 @@ def mlm_save():
         data = request.get_json(force=True) or {}
         source = data.get('source', '').strip()
         source_track_id = data.get('source_track_id', '').strip()
-        library_track_id = data.get('library_track_id')
+        library_track_id = mlm.normalize_library_track_id(data.get('library_track_id'))
         if not source or not source_track_id or not library_track_id:
             return jsonify({"success": False, "error": "source, source_track_id, library_track_id required"}), 400
-        try:
-            library_track_id = int(library_track_id)
-        except (TypeError, ValueError):
-            return jsonify({"success": False, "error": "Invalid library track id"}), 400
         db = get_database()
         profile_id = get_current_profile_id()
         # Validate library track exists before saving