diff --git a/build-constraints.yaml b/build-constraints.yaml
index fdc72f4b..91db8c69 100644
--- a/build-constraints.yaml
+++ b/build-constraints.yaml
@@ -1121,7 +1121,7 @@ packages:
         - hspec-wai-json
         - aeson-qq
         - interpolate
-        - doctest
+        - doctest < 0.21.0      # https://github.com/commercialhaskell/stackage/issues/6875
         - base-compat
 
     "Mario Blazevic <blamario@protonmail.com> @blamario":