diff --git a/noxfile.py b/noxfile.py
index 0e65692e..576a616c 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -79,7 +79,7 @@ def unitupb(session):
 def docs(session):
     """Build the docs."""
 
-    session.install("sphinx", "sphinx_rtd_theme")
+    session.install("sphinx==4.2.0", "sphinx_rtd_theme")
     session.install(".")
 
     # Build the docs!