diff --git a/pip-sample/requirements.txt b/pip-sample/requirements.txt
index 1d7c58ab9..f226bb143 100644
--- a/pip-sample/requirements.txt
+++ b/pip-sample/requirements.txt
@@ -26,7 +26,7 @@ kiwisolver==1.0.1
 mistune==0.8.3
 nbconvert==5.4.0
 nbformat==4.4.0
-nltk==3.3
+nltk==3.9.3
 notebook==5.7.0
 oauthlib==2.1.0
 pandocfilters==1.4.2