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diff --git a/testsuite/tests/indexed-types/should_compile/T4254.hs b/testsuite/tests/indexed-types/should_compile/T4254.hs
new file mode 100644
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+++ b/testsuite/tests/indexed-types/should_compile/T4254.hs
@@ -0,0 +1,16 @@
+{-# LANGUAGE TypeFamilies, FunctionalDependencies, RankNTypes, MultiParamTypeClasses #-}
+module T4254 where
+
+class FD a b | a -> b where
+  op :: a -> b;
+  op = undefined
+
+instance FD Int Bool
+
+ok1   :: forall a b. (a~Int,FD a b) => a -> b
+ok1    = op
+-- Should be OK: op has the right type
+
+ok2   :: forall a b. (a~Int,FD a b,b~Bool) => a -> Bool
+ok2    = op
+-- Should be OK: needs the b~Bool