diff --git a/doc/requirements.txt b/doc/requirements.txt
index 2eded3a..b84a3d1 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1 +1,3 @@
+sphinx >= 5, < 6
+docutils >= 0.18, < 0.20
 sphinx-last-updated-by-git