diff --git a/pyproject.toml b/pyproject.toml
index 2b594d0..d14d707 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,5 +1,5 @@
 [build-system]
-requires = ["flit_core >=2,<4"]
+requires = ["flit_core ==3.9.0"]
 build-backend = "flit_core.buildapi"
 
 [tool.flit.metadata]