diff --git a/beets/library.py b/beets/library.py
index f45e63ebe..ec530a5dd 100644
--- a/beets/library.py
+++ b/beets/library.py
@@ -1077,7 +1077,6 @@ class Item(LibModel):
         self,
         relative_to_libdir=False,
         basedir=None,
-        platform=None,
         path_formats=None,
     ) -> bytes:
         """Return the path in the library directory designated for the item
@@ -1087,7 +1086,6 @@ class Item(LibModel):
         library's base directory for the destination.
         """
         db = self._check_db()
-        platform = platform or sys.platform
         basedir = basedir or db.directory
         path_formats = path_formats or db.path_formats
 
@@ -1117,7 +1115,7 @@ class Item(LibModel):
         subpath = self.evaluate_template(subpath_tmpl, True)
 
         # Prepare path for output: normalize Unicode characters.
-        if platform == "darwin":
+        if sys.platform == "darwin":
             subpath = unicodedata.normalize("NFD", subpath)
         else:
             subpath = unicodedata.normalize("NFC", subpath)
diff --git a/test/test_library.py b/test/test_library.py
index 342c2fe20..a4e6dab44 100644
--- a/test/test_library.py
+++ b/test/test_library.py
@@ -23,6 +23,7 @@ import sys
 import time
 import unicodedata
 import unittest
+from unittest.mock import patch
 
 import pytest
 from mediafile import MediaFile, UnreadableFileError
@@ -411,13 +412,15 @@ class DestinationTest(BeetsTestCase):
     def test_unicode_normalized_nfd_on_mac(self):
         instr = unicodedata.normalize("NFC", "caf\xe9")
         self.lib.path_formats = [("default", instr)]
-        dest = self.i.destination(platform="darwin", relative_to_libdir=True)
+        with patch("sys.platform", "darwin"):
+            dest = self.i.destination(relative_to_libdir=True)
         assert as_string(dest) == unicodedata.normalize("NFD", instr)
 
     def test_unicode_normalized_nfc_on_linux(self):
         instr = unicodedata.normalize("NFD", "caf\xe9")
         self.lib.path_formats = [("default", instr)]
-        dest = self.i.destination(platform="linux", relative_to_libdir=True)
+        with patch("sys.platform", "linux"):
+            dest = self.i.destination(relative_to_libdir=True)
         assert as_string(dest) == unicodedata.normalize("NFC", instr)
 
     def test_non_mbcs_characters_on_windows(self):
@@ -436,7 +439,8 @@ class DestinationTest(BeetsTestCase):
     def test_unicode_extension_in_fragment(self):
         self.lib.path_formats = [("default", "foo")]
         self.i.path = util.bytestring_path("bar.caf\xe9")
-        dest = self.i.destination(platform="linux", relative_to_libdir=True)
+        with patch("sys.platform", "linux"):
+            dest = self.i.destination(relative_to_libdir=True)
         assert as_string(dest) == "foo.caf\xe9"
 
     def test_asciify_and_replace(self):