diff --git a/requirements_dev.txt b/requirements_dev.txt
index d504f233051..2554730f1a5 100644
--- a/requirements_dev.txt
+++ b/requirements_dev.txt
@@ -10,3 +10,4 @@ pytest>=4.5.0
 setuptools>=41.0.0
 sphinx-markdown-builder>=0.4.1
 Sphinx>=2.1.1
+mistune>=2.0.3 # not directly required, pinned by Snyk to avoid a vulnerability