diff --git a/.github/workflows/python-app.yml b/.github/workflows/python-app.yml
index 41240f8..de87672 100644
--- a/.github/workflows/python-app.yml
+++ b/.github/workflows/python-app.yml
@@ -23,7 +23,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8==2.5.4 pytest
+        pip install flake8==3.8.4 pytest
         if [ -f requirements.txt ]; then pip install -r requirements.txt; fi
     - name: Lint with flake8
       run: |
diff --git a/setup.py b/setup.py
index 498879d..9488cd2 100644
--- a/setup.py
+++ b/setup.py
@@ -50,7 +50,7 @@ class LintCommand(Command):
                 yield "%s.py" % filename
 
     def run(self):
-        from flake8.engine import get_style_guide
+        from flake8.api.legacy import get_style_guide
         flake8_style = get_style_guide(config_file='setup.cfg')
         paths = self.distribution_files()
         report = flake8_style.check_files(paths)
@@ -70,13 +70,13 @@ setup(
     zip_safe=False,
     include_package_data=True,
     setup_requires=[
-        'flake8',
+        'flake8>=3.8,<4',
     ],
     tests_require=[
-        'pytest',
+        'pytest>=6.2,<7',
     ],
     install_requires=[
-        'beautifulsoup4', 'six'
+        'beautifulsoup4>=4.9,<5', 'six>=1.15,<2'
     ],
     classifiers=[
         'Environment :: Web Environment',
@@ -87,6 +87,9 @@ setup(
         'Programming Language :: Python :: 2.5',
         'Programming Language :: Python :: 2.6',
         'Programming Language :: Python :: 2.7',
+        'Programming Language :: Python :: 3.6',
+        'Programming Language :: Python :: 3.7',
+        'Programming Language :: Python :: 3.8',
         'Topic :: Utilities'
     ],
     cmdclass={
diff --git a/tests/test_escaping.py b/tests/test_escaping.py
index 9b0d4fa..23a828c 100644
--- a/tests/test_escaping.py
+++ b/tests/test_escaping.py
@@ -2,7 +2,7 @@ from markdownify import markdownify as md
 
 
 def test_underscore():
-    assert md('_hey_dude_') == '\_hey\_dude\_'
+    assert md('_hey_dude_') == r'\_hey\_dude\_'
 
 
 def test_xml_entities():