diff --git a/src/flake8/main/options.py b/src/flake8/main/options.py
index f4588e8..a620ed9 100644
--- a/src/flake8/main/options.py
+++ b/src/flake8/main/options.py
@@ -156,6 +156,7 @@ def register_default_options(option_manager):
         default="",
         parse_from_config=True,
         comma_separated_list=True,
+        normalize_paths=True,
         help="Comma-separated list of files or directories to add to the list"
         " of excluded ones.",
     )
diff --git a/tests/integration/test_main.py b/tests/integration/test_main.py
index 54254ef..ab10bf9 100644
--- a/tests/integration/test_main.py
+++ b/tests/integration/test_main.py
@@ -114,7 +114,7 @@ def test_extend_exclude(tmpdir, capsys):
         tmpdir.mkdir(d).join('t.py').write('import os\nimport sys\n')
 
     with tmpdir.as_cwd():
-        _call_main(['--extend-exclude=vendor,legacy'], retv=1)
+        _call_main(['--extend-exclude=vendor,legacy/'], retv=1)
 
     out, err = capsys.readouterr()
     expected_out = '''\