diff --git a/build-constraints.yaml b/build-constraints.yaml
index 39e543060..cfd4696bf 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -5061,6 +5061,7 @@ packages:
 
     "James Cranch <cranch@cantab.net> @jcranch":
         - agreeing
+        - Mantissa
         - mappings
         - partialord
         - radix-tree