diff --git a/build-constraints.yaml b/build-constraints.yaml
index 7762a1604..49b02f8c9 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -115,7 +115,7 @@ packages:
         - java-adt
         - Sit
 
-        - alex
+        - alex < 3.5.2 # https://github.com/commercialhaskell/stackage/issues/7643
         - haskell-src
         - ListLike
         - MissingH