3 files changed, 48 insertions, 0 deletions
diff --git a/testsuite/tests/indexed-types/should_compile/T19336.hs b/testsuite/tests/indexed-types/should_compile/T19336.hs
new file mode 100644
index 0000000000..dfc7409fa3
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T19336.hs
@@ -0,0 +1,43 @@
+{-# LANGUAGE MultiParamTypeClasses, FlexibleContexts, FlexibleInstances
+           , DataKinds, NoMonomorphismRestriction, UndecidableInstances
+           , TypeFamilies #-}
+
+{-# OPTIONS_GHC -Wall #-}
+
+module T19336 where
+
+import GHC.TypeLits
+
+class X a b where
+  convert :: a -> b
+
+instance X Int String where
+  convert = show
+
+instance X String String where
+  convert = id
+
+instance {-# OVERLAPPABLE #-} TypeError ('Text "Oops") => X a b where
+  convert = error "unreachable"
+
+type family F a where
+  F String = String
+  F Int    = String
+
+convert_f :: X a (F a) => a -> a -> F a
+convert_f _ = convert
+
+----------
+
+class Poly a where
+  poly :: a
+
+instance Poly String where
+  poly = "hi"
+
+instance Poly Int where
+  poly = 2
+
+----------
+
+oops = convert_f poly
diff --git a/testsuite/tests/indexed-types/should_compile/T19336.stderr b/testsuite/tests/indexed-types/should_compile/T19336.stderr
new file mode 100644
index 0000000000..f841f79628
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T19336.stderr
@@ -0,0 +1,4 @@
+
+T19336.hs:43:1: warning: [-Wmissing-signatures (in -Wall)]
+    Top-level binding with no type signature:
+      oops :: (X a (F a), Poly a) => a -> F a
diff --git a/testsuite/tests/indexed-types/should_compile/all.T b/testsuite/tests/indexed-types/should_compile/all.T
index 469dd915df..7d8aa9f3ae 100644
--- a/testsuite/tests/indexed-types/should_compile/all.T
+++ b/testsuite/tests/indexed-types/should_compile/all.T
@@ -302,3 +302,4 @@ test('GivenLoop', normal, compile, [''])
 test('T18875', normal, compile, [''])
 test('T8707', normal, compile, ['-O'])
 test('T14111', normal, compile, ['-O'])
+test('T19336', normal, compile, ['-O'])