diff --git a/prepro/requirements.txt b/prepro/requirements.txt
old mode 100755
new mode 100644
index adc1d46..d8f638d
--- a/prepro/requirements.txt
+++ b/prepro/requirements.txt
@@ -46,7 +46,7 @@ Mako==1.0.7
 Markdown==3.0.1
 MarkupSafe==1.0
 matplotlib==3.0.1
-nltk==3.3
+nltk==3.4.5
 numpy==1.15.2
 oauth==1.0.1
 olefile==0.45.1