diff --git a/requirements.txt b/requirements.txt
index f86596f..99601a7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -30,7 +30,7 @@ MarkupSafe==0.23
 matplotlib==1.5.3
 more-itertools==2.4.1
 multidict==2.1.4
-nltk==3.2.1
+nltk==3.6.3
 numpy==1.11.3
 Pillow==3.4.2
 pyasn1==0.1.9