diff --git a/testsuite/tests/indexed-types/should_compile/T8889.hs b/testsuite/tests/indexed-types/should_compile/T8889.hs
new file mode 100644
index 0000000000000000000000000000000000000000..45c88a6a1857222770e9d95e3197e62093951fb1
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T8889.hs
@@ -0,0 +1,12 @@
+{-# LANGUAGE TypeFamilies, ConstraintKinds #-}
+{-# OPTIONS_GHC -fwarn-missing-signatures #-}  -- Report f's inferred type
+
+module T8889 where
+
+import GHC.Exts
+
+class C f where
+  type C_fmap f a :: Constraint
+  foo :: C_fmap f a => (a -> b) -> f a -> f b
+
+f x = foo x
diff --git a/testsuite/tests/indexed-types/should_compile/T8889.stderr b/testsuite/tests/indexed-types/should_compile/T8889.stderr
new file mode 100644
index 0000000000000000000000000000000000000000..77e05d764ba7188aa8a7214ffc87ae3511f87ba0
--- /dev/null
+++ b/testsuite/tests/indexed-types/should_compile/T8889.stderr
@@ -0,0 +1,6 @@
+
+T8889.hs:12:1: Warning:
+    Top-level binding with no type signature:
+      f :: forall (f :: * -> *) a b.
+           (C_fmap f a, C f) =>
+           (a -> b) -> f a -> f b
diff --git a/testsuite/tests/indexed-types/should_compile/all.T b/testsuite/tests/indexed-types/should_compile/all.T
index f722ea3b4f7f596dd2c772ed89f3cbf844a8cb02..5c156ec28e92f9d9008cb2cf17303a2ae70c4ecb 100644
--- a/testsuite/tests/indexed-types/should_compile/all.T
+++ b/testsuite/tests/indexed-types/should_compile/all.T
@@ -239,3 +239,4 @@ test('ClosedFam1', extra_clean(['ClosedFam1.o-boot', 'ClosedFam1.hi-boot']),
 test('ClosedFam2', extra_clean(['ClosedFam2.o-boot', 'ClosedFam2.hi-boot']),
      multimod_compile, ['ClosedFam2', '-v0'])
 test('T8651', normal, compile, [''])
+test('T8889', normal, compile, [''])