diff --git a/build-constraints.yaml b/build-constraints.yaml
index 8506c6c7a..52103b347 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -110,7 +110,7 @@ packages:
         - Sit
 
         - alex
-        - happy < 1.21.0 || > 1.21.0
+        - happy < 1.21.0 # Note, cannot use 1.21.0, and 2.0 blocked by https://github.com/commercialhaskell/stackage/issues/7520
         - haskell-src
         - ListLike
         - MissingH