diff --git a/pyproject.toml b/pyproject.toml
index c2da5ed..1866f81 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -32,6 +32,7 @@ dependencies = [
   "sortedcontainers-pydantic",
   "typenames",
   "typer",
+  "typing_extensions>4 ; python_version < '3.12'",
 ]
 
 [project.optional-dependencies]