diff --git a/doc/requirements.txt b/doc/requirements.txt
index de9a2f53ad..8e9df9687b 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -6,3 +6,4 @@ sphinx>=1.6.2 # BSD
 openstackdocstheme>=1.11.0 # Apache-2.0
 reno>=1.8.0  # Apache-2.0
 os-api-ref>=1.0.0 # Apache-2.0
+pygments>=2.7.4 # not directly required, pinned by Snyk to avoid a vulnerability