diff --git a/OP-GAN/requirements.txt b/OP-GAN/requirements.txt
index 7178d11..e497488 100644
--- a/OP-GAN/requirements.txt
+++ b/OP-GAN/requirements.txt
@@ -21,7 +21,7 @@ line-profiler==2.1.2
 matplotlib==3.0.3
 more-itertools==4.3.0
 networkx==2.3
-nltk==3.4.1
+nltk==3.4.5
 numpy==1.15.2
 parso==0.3.1
 pathlib2==2.3.2