diff --git a/brench/pyproject.toml b/brench/pyproject.toml
index 7b2508bee..1addf5174 100644
--- a/brench/pyproject.toml
+++ b/brench/pyproject.toml
@@ -1,6 +1,6 @@
 [build-system]
-requires = ["flit"]
-build-backend = "flit.buildapi"
+requires = ["flit_core >=2,<4"]
+build-backend = "flit_core.buildapi"
 
 [tool.flit.metadata]
 module = "brench"
diff --git a/bril-txt/pyproject.toml b/bril-txt/pyproject.toml
index 76727c87d..658e75d34 100644
--- a/bril-txt/pyproject.toml
+++ b/bril-txt/pyproject.toml
@@ -1,6 +1,6 @@
 [build-system]
-requires = ["flit"]
-build-backend = "flit.buildapi"
+requires = ["flit_core >=2,<4"]
+build-backend = "flit_core.buildapi"
 
 [tool.flit.metadata]
 module = "briltxt"