diff --git a/build-constraints.yaml b/build-constraints.yaml
index cf8b68de..8207ccbb 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -3078,6 +3078,9 @@ expected-test-failures:
 
     # https://github.com/beijaflor-io/haskell-language-dockerfile/issues/1
     - language-dockerfile
+
+    # https://github.com/JustusAdam/mustache/issues/21
+    - mustache
 # end of expected-test-failures
 
 # Benchmarks which are known not to build. Note that, currently we do not run