diff --git a/pyproject.toml b/pyproject.toml
index 729c2d5..ebfd0db 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -44,7 +44,7 @@ optional = true
 
 [tool.poetry.group.docs.dependencies]
 sphinx = ">=6,<8"
-sphinx-rtd-theme = ">=1.3,<3.0"
+sphinx-rtd-theme = ">=1.3,<4.0"
 certifi = ">=2018.4.16"
 expiringdict = ">=1.1.4"
 pyrfc3339 = ">=1.0"