diff --git a/docs/requirements.txt b/docs/requirements.txt
index 3818fe80ee..1855a346a3 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1 +1,2 @@
 breathe == 4.5.0
+sphinx>=3.0.4 # not directly required, pinned by Snyk to avoid a vulnerability