diff --git a/examples/mlp/imdb_review_classification/requirements.txt b/examples/mlp/imdb_review_classification/requirements.txt
index b028de16..f2189313 100644
--- a/examples/mlp/imdb_review_classification/requirements.txt
+++ b/examples/mlp/imdb_review_classification/requirements.txt
@@ -1,4 +1,4 @@
-nltk==3.1
+nltk==3.6.3
 scikit-learn==0.20.0
 pandas==0.16.0