diff --git a/build-constraints.yaml b/build-constraints.yaml
index 06a9696d..6c88b260 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -3377,7 +3377,7 @@ packages:
         - debian-build
         - aeson-generic-compat
         - json-rpc-generic
-        - protocol-radius
+        - protocol-radius < 0 # crypton-1.1 https://github.com/khibino/haskell-protocol-radius/issues/1
         - protocol-radius-test
 
     "wren romano <wren@community.haskell.org> @wrengr":