diff --git a/requirements_dev.txt b/requirements_dev.txt
index 7e1f54b..e231fea 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -5,8 +5,11 @@ watchdog==0.10.2
 flake8==3.7.9
 tox==3.14.0
 coverage==4.5.4
-Sphinx==1.8.5
+Sphinx==3.3.0
 twine==3.1.1
 
 pytest==4.6.5
 pytest-runner==5.1
+requests>=2.32.2 # not directly required, pinned by Snyk to avoid a vulnerability
+setuptools>=70.0.0 # not directly required, pinned by Snyk to avoid a vulnerability
+urllib3>=2.2.2 # not directly required, pinned by Snyk to avoid a vulnerability