diff --git a/requirements.txt b/requirements.txt
index cac5751..3e937f7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -12,6 +12,6 @@
 # pip install -r requirements.txt
 # Remember to also add them in setup.cfg but unpinned.
 # Example:
-nltk==3.4.5
+nltk==3.9
 scikit-learn==0.21.3