diff --git a/build-constraints.yaml b/build-constraints.yaml
index 11d41489..b7b65fcd 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -693,7 +693,7 @@ packages:
         - splitmix-distributions
         - rp-tree
         - xeno
-        - bytestring-mmap # required by xeno
+        - bytestring-mmap < 0 # required by xeno # not ghc 9.6 ready
         - datasets
         - lucid-extras
         - mnist-idx-conduit