diff --git a/beetsplug/smartplaylist.py b/beetsplug/smartplaylist.py
index 3a9f630ed..82739a995 100644
--- a/beetsplug/smartplaylist.py
+++ b/beetsplug/smartplaylist.py
@@ -57,8 +57,8 @@ class SmartPlaylistPlugin(BeetsPlugin):
         )
 
         self.config["prefix"].redact = True  # May contain username/password.
-        self._matched_playlists = None
-        self._unmatched_playlists = None
+        self._matched_playlists: set[tuple[Any, Any, Any]] = set()
+        self._unmatched_playlists: set[tuple[Any, Any, Any]] = set()
 
         if self.config["auto"]:
             self.register_listener("database_change", self.db_change)
@@ -129,15 +129,15 @@ class SmartPlaylistPlugin(BeetsPlugin):
     def update_cmd(self, lib: Any, opts: Any, args: list[str]) -> None:
         self.build_queries()
         if args:
-            args = set(args)
-            for a in list(args):
+            args_set = set(args)
+            for a in list(args_set):
                 if not a.endswith(".m3u"):
-                    args.add(f"{a}.m3u")
+                    args_set.add(f"{a}.m3u")
 
             playlists = {
                 (name, q, a_q)
                 for name, q, a_q in self._unmatched_playlists
-                if name in args
+                if name in args_set
             }
             if not playlists:
                 unmatched = [name for name, _, _ in self._unmatched_playlists]
@@ -185,6 +185,7 @@ class SmartPlaylistPlugin(BeetsPlugin):
             try:
                 for key, model_cls in (("query", Item), ("album_query", Album)):
                     qs = playlist.get(key)
+                    query_and_sort: tuple[Any, Any]
                     if qs is None:
                         query_and_sort = None, None
                     elif isinstance(qs, str):
@@ -353,7 +354,7 @@ class SmartPlaylistPlugin(BeetsPlugin):
                             )
                         f.write(comment.encode("utf-8") + entry.uri + b"\n")
             # Send an event when playlists were updated.
-            send_event("smartplaylist_update")
+            send_event("smartplaylist_update")  # type: ignore
 
         if pretend:
             self._log.info(
diff --git a/test/plugins/test_smartplaylist.py b/test/plugins/test_smartplaylist.py
index ad9f056cc..8ec2c74ce 100644
--- a/test/plugins/test_smartplaylist.py
+++ b/test/plugins/test_smartplaylist.py
@@ -33,8 +33,8 @@ from beetsplug.smartplaylist import SmartPlaylistPlugin
 class SmartPlaylistTest(BeetsTestCase):
     def test_build_queries(self):
         spl = SmartPlaylistPlugin()
-        assert spl._matched_playlists is None
-        assert spl._unmatched_playlists is None
+        assert spl._matched_playlists == set()
+        assert spl._unmatched_playlists == set()
 
         config["smartplaylist"]["playlists"].set([])
         spl.build_queries()
@@ -182,7 +182,7 @@ class SmartPlaylistTest(BeetsTestCase):
         q = Mock()
         a_q = Mock()
         pl = b"$title-my<playlist>.m3u", (q, None), (a_q, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         config["smartplaylist"]["relative_to"] = False
@@ -224,7 +224,7 @@ class SmartPlaylistTest(BeetsTestCase):
         q = Mock()
         a_q = Mock()
         pl = b"$title-my<playlist>.m3u", (q, None), (a_q, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         config["smartplaylist"]["output"] = "extm3u"
@@ -274,7 +274,7 @@ class SmartPlaylistTest(BeetsTestCase):
         q = Mock()
         a_q = Mock()
         pl = b"$title-my<playlist>.m3u", (q, None), (a_q, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         config["smartplaylist"]["output"] = "extm3u"
@@ -319,7 +319,7 @@ class SmartPlaylistTest(BeetsTestCase):
         q = Mock()
         a_q = Mock()
         pl = b"$title-my<playlist>.m3u", (q, None), (a_q, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         tpl = "http://beets:8337/item/$id/file"
@@ -380,7 +380,7 @@ class SmartPlaylistTest(BeetsTestCase):
         # Create playlist with multiple queries (stored as tuple)
         queries_and_sorts = ((q1, None), (q2, None), (q3, None))
         pl = "ordered.m3u", (queries_and_sorts, None), (None, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         config["smartplaylist"]["relative_to"] = False
@@ -435,7 +435,7 @@ class SmartPlaylistTest(BeetsTestCase):
         # Create playlist with multiple queries (stored as tuple)
         queries_and_sorts = ((q1, None), (q2, None))
         pl = "dedup.m3u", (queries_and_sorts, None), (None, None)
-        spl._matched_playlists = [pl]
+        spl._matched_playlists = {pl}
 
         dir = mkdtemp()
         config["smartplaylist"]["relative_to"] = False