diff --git a/requirements_dev_optional.txt b/requirements_dev_optional.txt
index 15b280e2b..523008fc3 100644
--- a/requirements_dev_optional.txt
+++ b/requirements_dev_optional.txt
@@ -14,7 +14,7 @@ pymongo==3.12.0
 # optional test requirements
 tox==3.24.4
 coverage
-flake8==3.9.2
+flake8==4.0.1
 pytest-cov==3.0.0
 pytest-doctestplus==0.11.0
 pytest-timeout==1.4.2