diff --git a/requirements_docs.txt b/requirements_docs.txt
index 75b22d35..89f8f52f 100644
--- a/requirements_docs.txt
+++ b/requirements_docs.txt
@@ -1,3 +1,4 @@
-Sphinx>=1.2.3
+Sphinx>=1.2.3 
+Sphinx<=5.1.1
 sphinx_rtd_theme
 .