diff --git a/notebook/requirements.txt b/notebook/requirements.txt
index 3375307..790e576 100644
--- a/notebook/requirements.txt
+++ b/notebook/requirements.txt
@@ -32,7 +32,7 @@ mistune==0.8.4
 more-itertools==8.3.0
 nbconvert==5.6.1
 nbformat==5.0.4
-nltk==3.5
+nltk==3.6.6
 notebook==6.1.5
 numpy==1.18.2
 packaging==20.4
diff --git a/requirements-train.txt b/requirements-train.txt
index 4e71271..4bb89d1 100644
--- a/requirements-train.txt
+++ b/requirements-train.txt
@@ -18,7 +18,7 @@ MarkupSafe==1.1.1
 matplotlib
 mccabe==0.6.1
 more-itertools==8.4.0
-nltk==3.5
+nltk==3.6.6
 numpy
 packaging==20.4
 pandas
diff --git a/requirements.txt b/requirements.txt
index f552ec5..09b9974 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,7 +13,7 @@ lazy-object-proxy==1.4.3
 MarkupSafe==1.1.1
 mccabe==0.6.1
 more-itertools==8.4.0
-nltk==3.5
+nltk==3.6.6
 numpy==1.18.5
 packaging==20.4
 pandas==1.0.4