diff --git a/mercurial/hgweb/request.py b/mercurial/hgweb/request.py
index 04d5cde28a7fc50d4c4d9b82a59d8bc767141654_bWVyY3VyaWFsL2hnd2ViL3JlcXVlc3QucHk=..9ed281bbf864f735d370ee0b76dbdc2d0fa1564b_bWVyY3VyaWFsL2hnd2ViL3JlcXVlc3QucHk= 100644
--- a/mercurial/hgweb/request.py
+++ b/mercurial/hgweb/request.py
@@ -11,7 +11,6 @@
 
 from ..thirdparty import attr
 from .. import (
-    encoding,
     error,
     pycompat,
     util,
@@ -167,13 +166,7 @@
     def tobytes(s):
         if not isinstance(s, str):
             return s
-        if pycompat.iswindows:
-            # This is what mercurial.encoding does for os.environ on
-            # Windows.
-            return encoding.strtolocal(s)
-        else:
-            # This is what is documented to be used for os.environ on Unix.
-            return pycompat.fsencode(s)
+        return s.encode('iso8859-1')
 
     env = {tobytes(k): tobytes(v) for k, v in env.items()}
 
diff --git a/tests/test-wsgirequest.py b/tests/test-wsgirequest.py
index 04d5cde28a7fc50d4c4d9b82a59d8bc767141654_dGVzdHMvdGVzdC13c2dpcmVxdWVzdC5weQ==..9ed281bbf864f735d370ee0b76dbdc2d0fa1564b_dGVzdHMvdGVzdC13c2dpcmVxdWVzdC5weQ== 100644
--- a/tests/test-wsgirequest.py
+++ b/tests/test-wsgirequest.py
@@ -500,16 +500,9 @@
         self.assertEqual(r.reponame, b'repo')
 
     def testenvencoding(self):
-        if pycompat.iswindows:
-            # On Windows, we can't generally know which non-ASCII characters
-            # are supported.
-            r = parse(DEFAULT_ENV, extra={'foo': 'bar'})
-            self.assertEqual(r.rawenv[b'foo'], b'bar')
-        else:
-            # Unix is byte-based. Therefore we test all possible bytes.
-            b = b''.join(pycompat.bytechr(i) for i in range(256))
-            r = parse(DEFAULT_ENV, extra={'foo': pycompat.fsdecode(b)})
-            self.assertEqual(r.rawenv[b'foo'], b)
+        b = b''.join(pycompat.bytechr(i) for i in range(256))
+        r = parse(DEFAULT_ENV, extra={'foo': b.decode('iso8859-1')})
+        self.assertEqual(r.rawenv[b'foo'], b)
 
 
 if __name__ == '__main__':