diff --git a/docs/rtd-requirements.txt b/docs/rtd-requirements.txt
index e2ea433..7f10599 100644
--- a/docs/rtd-requirements.txt
+++ b/docs/rtd-requirements.txt
@@ -1,6 +1,6 @@
 AccessControl==3.0.8
 Acquisition==2.13.8
-Babel==1.3
+Babel==2.9.1
 DateTime==3.0.3
 DocumentTemplate==2.13.2
 ExtensionClass==2.13.2