diff --git a/doc/requirements.txt b/doc/requirements.txt
index 548a9849..a78a8086 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -2,3 +2,4 @@ sphinx==3.4.3
 sphinx-rtd-theme>=0.5.2
 docutils>=0.14,<0.18
 Jinja2<3.1
+urllib3<2