diff --git a/build-constraints.yaml b/build-constraints.yaml
index cb458aca..d5632797 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -1509,6 +1509,9 @@ packages:
         # https://github.com/GaloisInc/cryptol/issues/275
         - cryptol < 5.0
 
+        # https://github.com/fpco/stackage/issues/856
+        - syb < 0.6
+
 # Package flags are applied to individual packages, and override the values of
 # global-flags
 package-flags: