diff --git a/setup.cfg b/setup.cfg
index ecb27ba..0292efc 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -51,7 +51,7 @@ docs =
     sphinx>=1.6
     sphinx-automodapi
     sphinx-subfigure
-    sphinx_rtd_theme<3
+    sphinx_rtd_theme<4
 
 broker =
     pyyaml
@@ -70,7 +70,7 @@ dev =
     sphinx>=1.6
     sphinx-automodapi
     sphinx-subfigure
-    sphinx_rtd_theme<3
+    sphinx_rtd_theme<4
     pylint
     black
     pypeit[specutils]>=1.15.0