diff --git a/crf/requirements.txt b/crf/requirements.txt
index 27e26b7..4fe7daa 100644
--- a/crf/requirements.txt
+++ b/crf/requirements.txt
@@ -1,4 +1,4 @@
-nltk == 3.2.2
+nltk == 3.4.5
 numpy == 1.12.1
 beautifulsoup4 == 4.6.0
 python_crfsuite == 0.9.2