diff --git a/src/csbot/config.py b/src/csbot/config.py
index 23fc81c..ee173b3 100644
--- a/src/csbot/config.py
+++ b/src/csbot/config.py
@@ -350,8 +350,8 @@ def _write(self, s, raw=False):
         """Write *s* to the current stream; if *raw* is True, don't apply comment filter."""
         if not raw and self._commented:
             lines = s.split("\n")
-            modified = [f"# {l}" if l and not l.startswith("#") else l
-                        for l in lines]
+            modified = [f"# {line}" if line and not line.startswith("#") else line
+                        for line in lines]
             s = "\n".join(modified)
         self._stream.write(s)
         self._at_start = False
diff --git a/src/csbot/util.py b/src/csbot/util.py
index 83fd2e0..740a5a9 100644
--- a/src/csbot/util.py
+++ b/src/csbot/util.py
@@ -134,14 +134,14 @@ def pairwise(iterable):
     return zip(a, b)
 
 
-def cap_string(s, l):
+def cap_string(s, n):
     """If a string is longer than a particular length,
     it gets truncated and has '...' added to the end.
     """
-    if len(s) <= l:
+    if len(s) <= n:
         return s
 
-    return s[0:l-3] + "..."
+    return s[0:n - 3] + "..."
 
 
 def ordinal(value):
diff --git a/tests/conftest.py b/tests/conftest.py
index 9da6e9d..9066f26 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -122,7 +122,7 @@ def receive(self, lines):
         """Shortcut to push a series of lines to the client."""
         if isinstance(lines, str):
             lines = [lines]
-        return [self.client.line_received(l) for l in lines]
+        return [self.client.line_received(line) for line in lines]
 
     def assert_sent(self, lines):
         """Check that a list of (unicode) strings have been sent.
@@ -132,7 +132,7 @@ def assert_sent(self, lines):
         """
         if isinstance(lines, str):
             lines = [lines]
-        self.client.send_line.assert_has_calls([mock.call(l) for l in lines])
+        self.client.send_line.assert_has_calls([mock.call(line) for line in lines])
         self.client.send_line.reset_mock()
 
 
diff --git a/tests/test_bot.py b/tests/test_bot.py
index ce398af..147dc35 100644
--- a/tests/test_bot.py
+++ b/tests/test_bot.py
@@ -188,7 +188,7 @@ def command_b(self, *args, **kwargs):
         def command_cd(self, *args, **kwargs):
             self.handler_mock(inspect.currentframe().f_code.co_name)
 
-    CONFIG_A = f"""\
+    CONFIG_A = """\
     ["@bot"]
     command_prefix = "&"
     plugins = ["mockplugin1"]
@@ -248,7 +248,7 @@ def __init__(self, *args, **kwargs):
         def command_a(self, *args, **kwargs):
             self.handler_mock(inspect.currentframe().f_code.co_name)
 
-    CONFIG_B = f"""\
+    CONFIG_B = """\
     ["@bot"]
     command_prefix = "&"
     plugins = ["mockplugin1", "mockplugin2"]
diff --git a/tests/test_config.py b/tests/test_config.py
index 949cd2a..b653b39 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -749,7 +749,7 @@ def _test_config_generator_list_wrap():
     class Config(config.Config):
         a = config.option_list(str, default=["abcdefghijklmnopqrstuvwxyz" for _ in range(2)], help="")
         b = config.option_list(str, default=["abcdefghijklmnopqrstuvwxyz" for _ in range(5)], help="")
-        abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz = config.option_list(str, help="")
+        abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz = config.option_list(str, help="")  # noqa: E501
 
     return Config, [
         # Shorter than threshold, don't split
@@ -763,7 +763,7 @@ class Config(config.Config):
         '  "abcdefghijklmnopqrstuvwxyz",',
         ']',
         # Key longer than threshold, but no items, don't split
-        'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz = []',
+        'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz = []',  # noqa: E501
     ]
 
 
diff --git a/tests/test_plugin_github.py b/tests/test_plugin_github.py
index 3be1a8e..a166e48 100644
--- a/tests/test_plugin_github.py
+++ b/tests/test_plugin_github.py
@@ -67,8 +67,8 @@ class TestGitHubPlugin:
 
     ["github/alanbriolat/csbot-webhook-test"]
     notify = "#mychannel"
-    """
-    URL = f'/webhook/github/foobar'
+    """  # noqa: E501
+    URL = '/webhook/github/foobar'
     pytestmark = pytest.mark.bot(plugins=PLUGINS, config=CONFIG)
 
     TEST_CASES = [
diff --git a/tests/test_plugin_linkinfo.py b/tests/test_plugin_linkinfo.py
index 14f105c..d7726fa 100644
--- a/tests/test_plugin_linkinfo.py
+++ b/tests/test_plugin_linkinfo.py
@@ -221,7 +221,7 @@ def __init__(self, *args, **kwargs):
         def privmsg(self, event):
             self.handler_mock(event['message'])
 
-    CONFIG = f"""\
+    CONFIG = """\
     ["@bot"]
     plugins = ["mockplugin", "linkinfo"]
     """
diff --git a/tox.ini b/tox.ini
index 36c50f0..b349a89 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,7 +6,7 @@ skipsdist = True
 passenv = TRAVIS TRAVIS_* GITHUB_*
 deps =
     -r requirements.txt
-    flake8: flake8
+    flake8: flake8==4.0.1
 commands =
     python -m pytest {posargs}
-    flake8: flake8 --exit-zero --exclude=src/csbot/plugins_broken src/ tests/
+    flake8: flake8 --exclude=src/csbot/plugins_broken src/ tests/