diff --git a/build-constraints.yaml b/build-constraints.yaml
index 4f01d5f9..fb713411 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -811,7 +811,7 @@ packages:
         - foreign-store
         - formatting
         - gtk2hs-buildtools
-        - happy < 1.21.0 || > 1.21.0
+        - happy < 1.20.1 || > 1.21.0
         - hybrid-vectors
         - indents
         - language-c