diff --git a/nlp/chatbots/requirements.txt b/nlp/chatbots/requirements.txt
old mode 100755
new mode 100644
index 95ddd62..f1e2cd8
--- a/nlp/chatbots/requirements.txt
+++ b/nlp/chatbots/requirements.txt
@@ -5,3 +5,4 @@ chatterbot_corpus
 numpy
 sklearn
 nltk
+tornado>=6.4.1 # not directly required, pinned by Snyk to avoid a vulnerability