diff --git a/build-constraints.yaml b/build-constraints.yaml
index 48fcbd1a..f7183923 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -1452,6 +1452,7 @@ packages:
     "Index Int <vlad.z.4096@gmail.com>":
         - transformers-lift
         - ether
+        - union
 
     "Stack Builders stackage@stackbuilders.com @stackbuilders":
         - hapistrano