diff --git a/testsuite/tests/typecheck/should_compile/T17873.hs b/testsuite/tests/typecheck/should_compile/T17873.hs
new file mode 100644
index 0000000000000000000000000000000000000000..3372f62bfd81f3dfef986e1b3bf9c1678751f917
--- /dev/null
+++ b/testsuite/tests/typecheck/should_compile/T17873.hs
@@ -0,0 +1,15 @@
+{-# LANGUAGE ImplicitParams #-}
+
+module T17873 where
+
+-- With GHC 8.8 this failed with a nonsense message
+--    Couldn't match type ‘?x::Bool -> Bool’ with ‘Bool’
+--      Expected type: Bool -> Bool -> Bool
+--      Actual type: (?x::Bool -> Bool) => Bool -> Bool
+
+-- With eager instantiation, it's fine.
+
+getx :: (?x :: Bool -> Bool) => Bool -> Bool
+getx = ?x
+
+z3 = (let ?x = not in getx) False
diff --git a/testsuite/tests/typecheck/should_compile/all.T b/testsuite/tests/typecheck/should_compile/all.T
index a7825b9f5441cd85c142fc26bdad8cc85a2b06f3..03389993ddffc79ed920607754e1ec38e43c6416 100644
--- a/testsuite/tests/typecheck/should_compile/all.T
+++ b/testsuite/tests/typecheck/should_compile/all.T
@@ -705,3 +705,4 @@ test('T18005', normal, compile, [''])
 test('T18023', normal, compile, [''])
 test('T18036', normal, compile, [''])
 test('T18036a', normal, compile, [''])
+test('T17873', normal, compile, [''])