diff --git a/build-constraints.yaml b/build-constraints.yaml
index 1f86a3e9..ca0f9b45 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -8473,6 +8473,7 @@ expected-test-failures:
     - users-persistent # sqlite
     - users-postgresql-simple # PostgreSQL
     - wai-cors # PhantomJS
+    - wai-middleware-delegate # Access to httpbin.org is unreliable (at the moment 504 Gateway Time-out).
     - wai-rate-limit-redis # Redis
     - wai-session-postgresql # PostgreSQL
     - wai-session-redis # https://github.com/commercialhaskell/stackage/pull/5980