diff --git a/build-constraints.yaml b/build-constraints.yaml
index 815525d5..b4872260 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -598,7 +598,7 @@ packages:
         - incremental-parser
         - monoid-subclasses
         - picoparsec
-        # - rank2classes # doctest https://github.com/fpco/stackage/pull/3122
+        - rank2classes
 
     "Brent Yorgey <byorgey@gmail.com> @byorgey":
         - active