diff --git a/pyproject.toml b/pyproject.toml
index 5a36d88b..b9d19ef8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -34,6 +34,7 @@ keywords = [
 ]
 requires-python = ">=3.7"
 dependencies = [
+    "attrs>=19",
     "docutils>=0.15,<0.18",
     "jinja2", # required for substitutions, but let sphinx choose version
     "markdown-it-py>=1.0.0,<3.0.0",