diff --git a/build-constraints.yaml b/build-constraints.yaml
index ddbdc7b7..01935e8c 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -930,6 +930,7 @@ packages:
 
         # Force a specific version that's compatible with transformers 0.3
         - transformers-compat == 0.4.0.3
+        - mtl-compat == 0.2.1.1
 
         # https://github.com/fpco/stackage/issues/476
         - vector-space < 0.10