diff --git a/requirements.txt b/requirements.txt
index a0f5fe5..a08f68c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -7,3 +7,4 @@ scikit_learn==0.22.1
 flask==1.1.1
 chatterbot==1.0.5
 chatterbot-corpus==1.2.0
+pyyaml>=5.2 # not directly required, pinned by Snyk to avoid a vulnerability