diff --git a/build-constraints.yaml b/build-constraints.yaml
index 4814810f..e9dea1f0 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -5248,6 +5248,7 @@ packages:
         - currycarbon
 
     "Benjamin Orchard <thefirstmuffinman@gmail.com> @raehik":
+        - defun-core # https://github.com/phadej/defun/issues/4
         - flatparse
         - strongweak
         - mason