diff --git a/pyproject.toml b/pyproject.toml
index 66349f6..5b48fac 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [build-system]
-requires = ["flit"]
-build-backend = "flit.buildapi"
+requires = ["flit_core >=2,<4"]
+build-backend = "flit_core.buildapi"
 
 [project]
 name =  "specarray"