diff --git a/tox.ini b/tox.ini
index ed7e548d2..b41164d32 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,7 +17,7 @@ commands =
 
 [testenv:flake8]
 deps =
-  flake8>=3.8.4,<5.1
+  flake8>=3.8.4,<6.1
   flake8-tidy-imports>=4.2.0,<5
 commands =
   flake8 --jobs 8 mitmproxy examples test release {posargs}