diff --git a/music_curator.py b/music_curator.py
index dd7696a..f8d5d47 100644
--- a/music_curator.py
+++ b/music_curator.py
@@ -75,6 +75,11 @@ PLAYLIST_DIRECTORY = "_playlists"
 # library holds Mötley Crüe, Beyoncé and Sigur Rós.
 PLAYLIST_SUFFIX = ".m3u8"
 
+# Extensions this tool has written in the past. A playlist of the same name
+# under one of these is a leftover of its own, and is cleaned up even though no
+# record of writing it survives.
+SUPERSEDED_SUFFIXES = (".m3u",)
+
 # Tags are re-fetched this often. They move slowly, and the first pass over a
 # library already costs one request per artist.
 TAG_REFRESH_SECONDS = 90 * 86400
@@ -1674,9 +1679,22 @@ def prune_playlists(directory, produced, store):
     Driven by a record of what was written last time rather than by "every M3U
     that is not one of ours", so a playlist put there by hand is left alone. A
     renamed mood otherwise leaves its old file on the device for ever.
+
+    That record cannot reach back before it existed, which is how the switch
+    from .m3u to .m3u8 left every playlist on the device twice: the old files
+    were written by a version that kept no record, so there was nothing to
+    prune them by. A file with the same name as one being written now, under a
+    superseded extension, is therefore removed as well -- narrow enough that
+    only this tool's own leavings match it.
     """
     previous = set(json.loads(store.get_state("playlist_files") or "[]"))
-    for name in sorted(previous - set(produced)):
+    stale_names = previous - set(produced)
+    for name in produced:
+        for superseded in SUPERSEDED_SUFFIXES:
+            stale_names.add(Path(name).with_suffix(superseded).name)
+    stale_names -= set(produced)
+
+    for name in sorted(stale_names):
         stale = directory / name
         if stale.is_file():
             logger.info("removing playlist %s, no longer produced", name)
diff --git a/tests/test_music_curator.py b/tests/test_music_curator.py
index 788ff77..dde613d 100644
--- a/tests/test_music_curator.py
+++ b/tests/test_music_curator.py
@@ -1504,3 +1504,35 @@ def test_the_old_m3u_playlists_are_pruned_after_the_rename(tmp_path):
     music_curator.prune_playlists(directory, ["screamo.m3u8"], store)
 
     assert not (directory / "screamo.m3u").exists()
+
+
+def test_a_playlist_under_a_superseded_extension_is_removed(tmp_path):
+    """Switching from .m3u to .m3u8 left every playlist on the device twice.
+    The old files predated the record of what had been written, so there was
+    nothing to prune them by."""
+    api, source, mirror = playlist_library(tmp_path)
+    store = store_at(tmp_path)
+    directory = mirror / "_playlists"
+    directory.mkdir(parents=True, exist_ok=True)
+    (directory / "screamo.m3u").write_text("#EXTM3U\n")
+    (directory / "screamo.m3u8").write_text("#EXTM3U\n")
+
+    # No record at all, as on the first run after the rename.
+    music_curator.prune_playlists(directory, ["screamo.m3u8"], store)
+
+    assert not (directory / "screamo.m3u").exists()
+    assert (directory / "screamo.m3u8").is_file()
+
+
+def test_an_unrelated_m3u_is_still_left_alone(tmp_path):
+    """Only a name this run is writing anyway is matched, so a playlist made by
+    hand survives whatever its extension."""
+    api, source, mirror = playlist_library(tmp_path)
+    store = store_at(tmp_path)
+    directory = mirror / "_playlists"
+    directory.mkdir(parents=True, exist_ok=True)
+    (directory / "lyras-own-mix.m3u").write_text("#EXTM3U\n")
+
+    music_curator.prune_playlists(directory, ["screamo.m3u8"], store)
+
+    assert (directory / "lyras-own-mix.m3u").is_file()