diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index c0ff14f80..c2cbe6403 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -118,6 +118,11 @@ lint:
   script:
     - tox -e lint
 
+invalidcode:
+  extends: .lint-stage
+  script:
+    - tox -e invalidcode
+
 # Disabled, waiting for buster
 #format-check:
 #  extends: .lint-stage
diff --git a/src/yunohost/app.py b/src/yunohost/app.py
index 34a2381d7..950d0b401 100644
--- a/src/yunohost/app.py
+++ b/src/yunohost/app.py
@@ -926,12 +926,12 @@ def dump_app_log_extract_for_debugging(operation_logger):
         r"ynh_script_progression"
     ]
 
-    filters = [re.compile(f) for f in filters]
+    filters = [re.compile(f_) for f_ in filters]
 
     lines_to_display = []
     for line in lines:
 
-        if not ": " in line.strip():
+        if ": " not in line.strip():
             continue
 
         # A line typically looks like
diff --git a/src/yunohost/domain.py b/src/yunohost/domain.py
index 700505d54..acd4a1131 100644
--- a/src/yunohost/domain.py
+++ b/src/yunohost/domain.py
@@ -534,10 +534,10 @@ def _build_dns_conf(domain, ttl=3600, include_empty_AAAA_if_no_ipv6=False):
     ####################
 
     records = {
-        "basic": [{"name": name, "ttl": ttl, "type": type_, "value": value} for name, ttl, type_, value in basic],
-        "xmpp": [{"name": name, "ttl": ttl, "type": type_, "value": value} for name, ttl, type_, value in xmpp],
-        "mail": [{"name": name, "ttl": ttl, "type": type_, "value": value} for name, ttl, type_, value in mail],
-        "extra": [{"name": name, "ttl": ttl, "type": type_, "value": value} for name, ttl, type_, value in extra],
+        "basic": [{"name": name, "ttl": ttl_, "type": type_, "value": value} for name, ttl_, type_, value in basic],
+        "xmpp": [{"name": name, "ttl": ttl_, "type": type_, "value": value} for name, ttl_, type_, value in xmpp],
+        "mail": [{"name": name, "ttl": ttl_, "type": type_, "value": value} for name, ttl_, type_, value in mail],
+        "extra": [{"name": name, "ttl": ttl_, "type": type_, "value": value} for name, ttl_, type_, value in extra],
     }
 
     ##################
diff --git a/src/yunohost/service.py b/src/yunohost/service.py
index c17eb04c2..029ecf77c 100644
--- a/src/yunohost/service.py
+++ b/src/yunohost/service.py
@@ -26,7 +26,6 @@
 
 import re
 import os
-import re
 import time
 import yaml
 import subprocess
diff --git a/tox.ini b/tox.ini
index ac109609c..8d033367b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,7 @@ skip_install=True
 deps =
   pytest >= 4.6.3, < 5.0
   pyyaml >= 5.1.2, < 6.0
+  flake8 >= 3.7.9, < 3.8
 commands =
     pytest {posargs}
 
@@ -16,3 +17,8 @@ commands =
 skip_install=True
 commands = flake8 src doc data tests
 deps = flake8
+
+[testenv:invalidcode]
+skip_install=True
+commands = flake8 src data --exclude src/yunohost/tests --select F --ignore F401,F841
+deps = flake8