1 files changed, 24 insertions, 0 deletions
diff --git a/testsuite/tests/typecheck/should_compile/T21909.hs b/testsuite/tests/typecheck/should_compile/T21909.hs
new file mode 100644
index 0000000000..2485134703
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T21909.hs
@@ -0,0 +1,24 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE UndecidableSuperClasses #-}
+
+module T21909 where
+
+import Data.Kind
+
+class (Monad m, MyMonad (Inner m)) => MyMonad m where
+  type Inner m :: Type -> Type
+  foo :: m Int
+
+works :: MyMonad m => m String
+works = show <$> ((+ 1) <$> foo)
+
+fails :: MyMonad m => m String
+fails = show <$> fooPlusOne
+  where
+    fooPlusOne = (+ 1) <$> foo
+
+alsoFails :: MyMonad m => m String
+alsoFails =
+  let fooPlusOne = (+ 1) <$> foo
+   in show <$> fooPlusOne