diff --git a/build-constraints.yaml b/build-constraints.yaml
index d97972c7..1d0787e0 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -4577,7 +4577,7 @@ packages:
         - th-test-utils
 
     "Brandon Chinn <brandonchinn178@gmail.com> @brandonchinn178":
-        - fourmolu
+        - fourmolu < 0.12 # https://github.com/commercialhaskell/stackage/issues/6949
         - http-api-data-qq
         - persistent-mtl
         - tasty-autocollect