diff --git a/build-constraints.yaml b/build-constraints.yaml
index 56f6aa05..a06d5c7e 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -5255,7 +5255,7 @@ expected-test-failures:
     - perf # https://github.com/fpco/stackage/pull/2859
     - picosat # https://github.com/fpco/stackage/pull/2382
     - pkcs10 # https://github.com/fcomb/pkcs10-hs/issues/2
-    - polysemy-zoo # TODO: add link here
+    - polysemy-zoo # https://github.com/isovector/polysemy-zoo/issues/21
     - sourcemap # https://github.com/chrisdone/sourcemap/issues/3
     - squeal-postgresql # https://github.com/fpco/stackage/issues/3180
     - text-icu # https://github.com/bos/text-icu/issues/32