diff --git a/build-constraints.yaml b/build-constraints.yaml
index d325a14d1..61a384e0e 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -5243,7 +5243,7 @@ packages:
 
     "Sebastian Graf <sgraf1337@gmail.com> @sgraf812":
         - happy-lib
-        - happy
+        - happy < 1.21 # Note, cannot use 1.21.0
 
     "Grandfathered dependencies":
         - BiobaseNewick