diff --git a/pyproject.toml b/pyproject.toml
index 9a063348..228f4a34 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -101,7 +101,7 @@ addopts = "--ignore-glob 'tests/my_*.py'"
 [tool.pdm.dev-dependencies]
 tests = [
     "pytest",
-    "pytest-asyncio",
+    "pytest-asyncio==0.21.1",
     "pytest-httpx",
     "pytest-cov",
     "fastapi",