diff --git a/NLPyPort/requirements.txt b/NLPyPort/requirements.txt
index c7766d6..6547608 100644
--- a/NLPyPort/requirements.txt
+++ b/NLPyPort/requirements.txt
@@ -1,4 +1,4 @@
-nltk==3.4
+nltk==3.4.5
 numpy==1.16.2
 pandas==0.24.2
 python-crfsuite==0.9.6