diff --git a/pyproject.toml b/pyproject.toml
index fce8eb61..49313745 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,7 +50,7 @@ complete = [
     "boto3>=1.14.44",
     "dask",
     "distributed",
-    "Flask",
+    "Flask<3.0.0",
     "Flask-RangeRequest",
     "fsspec[http]",
     "fsspec[s3]",