1 files changed, 22 insertions, 0 deletions
diff --git a/testsuite/tests/generics/T21185.hs b/testsuite/tests/generics/T21185.hs
new file mode 100644
index 0000000000..1d2d1f30af
--- /dev/null
+++ b/testsuite/tests/generics/T21185.hs
@@ -0,0 +1,22 @@
+{-# LANGUAGE TypeFamilies #-}
+module T21185 where
+
+import Data.Kind (Type)
+import GHC.Generics (Generic1(..))
+
+type FakeOut x = Int
+
+data D (b :: Type) where
+  MkD :: c -> FakeOut c -> D c
+  deriving Generic1
+
+data family DF (a :: Type)
+data instance DF (b :: Type) where
+  MkDF :: c -> FakeOut c -> DF c
+  deriving Generic1
+
+d :: Rep1 D ()
+d = from1 $ MkD () 42
+
+df :: Rep1 DF ()
+df = from1 $ MkDF () 42