diff --git a/build-constraints.yaml b/build-constraints.yaml
index a5682a0d..66c71a2d 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -3836,6 +3836,7 @@ packages:
         - hspec-discover < 2.5.6
         - hspec-meta < 2.5.6
         - hspec-contrib < 0.5.1
+        - cassava-conduit < 0.5.1 # https://github.com/commercialhaskell/stackage/pull/4139#issuecomment-443035843
 
         # https://github.com/commercialhaskell/stackage/issues/4053
         - yaml < 0.11