diff --git a/pyproject.toml b/pyproject.toml
index 9b8b80f..e949b4f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -68,7 +68,7 @@ pyupgrade = "^2.29.0"
 optional = true
 
 [tool.poetry.group.docs.dependencies]
-sphinx  = "^4.3.2"
+sphinx  = ">=4.3.2,<7.0.0"
 sphinx_book_theme = ">= 1.0.1, < 2.0"
 sphinx-copybutton = "*"
 docutils = "*"