diff --git a/docs/source/requirements.txt b/docs/source/requirements.txt
index a57363e..3b64c4f 100644
--- a/docs/source/requirements.txt
+++ b/docs/source/requirements.txt
@@ -1,2 +1,3 @@
-docutils>0.18,!=0.18.1,<=0.20.1
+docutils>=0.18,!=0.18.1,<=0.20.1
 pillow>=6.2.0
+sphinx-rtd-theme>=2.0.0