diff --git a/setup.cfg b/setup.cfg
index 5fc43b51..7de4bad2 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -3,7 +3,6 @@ universal = 1
 
 [flake8]
 max-line-length = 140
-exclude = tests/*,*/migrations/*,*/south_migrations/*
 
 [tool:pytest]
 testpaths = tests
diff --git a/tests/test_pytest_cov.py b/tests/test_pytest_cov.py
index 8809eaed..bac073ed 100644
--- a/tests/test_pytest_cov.py
+++ b/tests/test_pytest_cov.py
@@ -152,6 +152,23 @@ def test_foo(cov):
 xdist_params = pytest.mark.parametrize('opts', ['', '-n 1'], ids=['nodist', 'xdist'])
 
 
+@pytest.fixture(scope='session', autouse=True)
+def adjust_sys_path():
+    """Adjust PYTHONPATH during tests to make "helper" importable in SCRIPT."""
+    orig_path = os.environ.get('PYTHONPATH', None)
+    new_path = os.path.dirname(__file__)
+    if orig_path is not None:
+        new_path = os.pathsep.join([new_path, orig_path])
+    os.environ['PYTHONPATH'] = new_path
+
+    yield
+
+    if orig_path is None:
+        del os.environ['PYTHONPATH']
+    else:
+        os.environ['PYTHONPATH'] = orig_path
+
+
 @pytest.fixture(params=[
     ('branch=true', '--cov-branch', '9 * 85%', '3 * 100%'),
     ('branch=true', '',             '9 * 85%', '3 * 100%'),
@@ -450,7 +467,8 @@ def test_subprocess_with_path_aliasing(testdir, monkeypatch):
 parallel = true
 """)
 
-    monkeypatch.setitem(os.environ, 'PYTHONPATH', os.pathsep.join([os.environ.get('PYTHONPATH',''), 'aliased']))
+    monkeypatch.setitem(os.environ, 'PYTHONPATH', os.pathsep.join([
+        os.environ.get('PYTHONPATH', ''), 'aliased']))
     result = testdir.runpytest('-v',
                                '--cov',
                                '--cov-report=term-missing',
@@ -1112,6 +1130,7 @@ def test_run():
     ])
     assert result.ret == 0
 
+
 @pytest.mark.skipif('sys.platform == "win32"', reason="fork not available on Windows")
 def test_cleanup_on_sigterm_sig_ign(testdir):
     script = testdir.makepyfile('''
@@ -1235,7 +1254,7 @@ def test_no_cover_marker(testdir):
 @pytest.mark.no_cover
 def test_basic():
     mod.func()
-    subprocess.check_call([sys.executable, '-c', 'from mod import func; func()'])    
+    subprocess.check_call([sys.executable, '-c', 'from mod import func; func()'])
 ''')
     result = testdir.runpytest('-v', '-ra', '--strict',
                                '--cov=%s' % script.dirpath(),
@@ -1254,7 +1273,7 @@ def test_no_cover_fixture(testdir):
 
 def test_basic(no_cover):
     mod.func()
-    subprocess.check_call([sys.executable, '-c', 'from mod import func; func()'])    
+    subprocess.check_call([sys.executable, '-c', 'from mod import func; func()'])
 ''')
     result = testdir.runpytest('-v', '-ra', '--strict',
                                '--cov=%s' % script.dirpath(),
diff --git a/tox.ini b/tox.ini
index 8b15169f..dc80c8b7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -18,7 +18,6 @@ basepython =
     py37: {env:TOXPYTHON:python3.7}
     {clean,check,report,extension-coveralls,coveralls,spell}: python3.4
 setenv =
-    PYTHONPATH={toxinidir}/tests
     PYTHONUNBUFFERED=yes
 passenv =
     *