diff --git a/doc/requirements.txt b/doc/requirements.txt
index 4179db2..de11701 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,4 +1,4 @@
-Babel==2.8.0
+Babel==2.9.1
 click==7.1.1
 Flask==0.12.2
 Flask-Babel==0.11.2