diff --git a/packages/python/pyproject.toml b/packages/python/pyproject.toml
index a3cf503..0e340cb 100644
--- a/packages/python/pyproject.toml
+++ b/packages/python/pyproject.toml
@@ -27,7 +27,7 @@ classifiers = [
   "Programming Language :: Python :: Implementation :: CPython",
   "Programming Language :: Python :: Implementation :: PyPy",
 ]
-dependencies = ["attrs", "cattrs"]
+dependencies = ["attrs>=21.3.0", "cattrs"]
 
 [project.urls]
 Issues = "https://github.com/microsoft/lsprotocol/issues"