1 files changed, 26 insertions, 0 deletions
diff --git a/testsuite/tests/unboxedsums/T20858.hs b/testsuite/tests/unboxedsums/T20858.hs
new file mode 100644
index 0000000000..cada160764
--- /dev/null
+++ b/testsuite/tests/unboxedsums/T20858.hs
@@ -0,0 +1,26 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE ExplicitForAll #-}
+{-# LANGUAGE MagicHash #-}
+{-# LANGUAGE PolyKinds #-}
+{-# LANGUAGE StandaloneKindSignatures #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UnboxedSums #-}
+
+module T20858 where
+
+import Data.Kind
+  ( Type )
+import GHC.Exts
+  ( Double#, Int#, Word# )
+
+type GetFunKind :: k -> Type
+type family GetFunKind x where
+  forall arg_k res_k (a :: arg_k -> res_k) (b :: arg_k). GetFunKind (a b) = arg_k -> res_k
+
+type GetFun :: forall res_k. forall (x :: res_k) -> GetFunKind x
+type family GetFun x where
+  GetFun (a b) = a
+
+type S1 = GetFun (# Int# | Double# | Word# #)
+type S2 = GetFun S1
+type S3 = GetFun S2