diff --git a/requirements.txt b/requirements.txt
index abdedbd..00cb928 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -81,7 +81,7 @@ nbconvert==4.1.0
 nbformat==4.0.1
 networkx==1.11
 nibabel==2.1.0.dev0
-nltk==3.2
+nltk==3.6.3
 nolearn==0.6a0.dev0
 nose==1.3.7
 notebook==4.1.0