diff --git a/pyproject.toml b/pyproject.toml
index 3a8601b3..ef8678a9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,6 +35,7 @@ classifiers = [
 ]
 dependencies = [
     "anyio >=3.4.0,<5.0",
+    "sniffio >=1.1",
     "typing_extensions >=4.8.0; python_version < '3.10'"
 ]