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diff --git a/testsuite/tests/typecheck/should_fail/tcfail096.hs b/testsuite/tests/typecheck/should_fail/tcfail096.hs
new file mode 100644
index 0000000000..8a4edfbc6c
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/tcfail096.hs
@@ -0,0 +1,25 @@
+{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
+             FlexibleInstances #-}
+module ShouldFail where
+
+class Foo f a r | f a -> r where
+      foo::f->a->r
+
+-- These instances are incompatible because we can unify
+-- the first two paramters, though it's rather obscure:
+--	p -> (a,b)
+--	t -> (,) (a,a)
+--	c -> (,) a
+--	r -> s
+--
+-- So a constraint which would sow this up is
+--	Foo ((Int,Int)->Int)
+--	    ((Int,Int), (Int,Int))
+--	    t
+-- This matches both.  Not easy to spot, and the error
+-- message would be improved by giving the unifier, or
+-- a witness.
+
+instance Foo (p->s)     (t p)    (t s)
+instance Foo ((a,b)->r) (c a,c b)(c r)
+