3 files changed, 52 insertions, 0 deletions
diff --git a/testsuite/tests/patsyn/should_fail/T14552.hs b/testsuite/tests/patsyn/should_fail/T14552.hs
new file mode 100644
index 0000000000..a4a7493530
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T14552.hs
@@ -0,0 +1,43 @@
+{-# Language RankNTypes, ViewPatterns, PatternSynonyms, TypeOperators, ScopedTypeVariables,
+             KindSignatures, PolyKinds, DataKinds, TypeFamilies, GADTs #-}
+
+module T14552 where
+
+import Data.Kind
+import Data.Proxy
+
+data family Sing a
+
+type a --> b = (a, b) -> Type
+
+type family F (f::a --> b) (x::a) :: b
+
+newtype Limit :: (k --> Type) -> Type where
+  Limit :: (forall xx. Proxy xx -> F f xx) -> Limit f
+
+data Exp :: [Type] -> Type -> Type where
+  TLam :: (forall aa. Proxy aa -> Exp xs (F w aa))
+        -> Exp xs (Limit w)
+
+pattern FOO f <- TLam (($ Proxy) -> f)
+
+
+{-
+TLam :: forall (xs::[Type]) (b::Type).   -- Universal
+         forall k (w :: k --> Type).      -- Existential
+         (b ~ Limit w) =>
+         => (forall (aa :: k). Proxy aa -> Exp xs (F w aa))
+         -> Exp xs b
+
+-}
+
+{-
+mfoo :: Exp xs b
+     -> (forall k (w :: k --> Type).
+         (b ~ Limit w)
+         => Exp xs (F w aa)
+         -> r)
+     -> r
+mfoo scrut k = case srcut of
+                 TLam g -> k (g Proxy)
+-}
diff --git a/testsuite/tests/patsyn/should_fail/T14552.stderr b/testsuite/tests/patsyn/should_fail/T14552.stderr
new file mode 100644
index 0000000000..b9b6b8448b
--- /dev/null
+++ b/testsuite/tests/patsyn/should_fail/T14552.stderr
@@ -0,0 +1,8 @@
+
+T14552.hs:22:9: error:
+    • Cannot generalise type; skolem ‘k’ would escape its scope
+      if I tried to quantify (aa0 :: k) in this type:
+        forall k (w :: k --> *). Exp a0 (F @k @(*) w aa0)
+      (Indeed, I sometimes struggle even printing this correctly,
+       due to its ill-scoped nature.)
+    • In the declaration for pattern synonym ‘FOO’
diff --git a/testsuite/tests/patsyn/should_fail/all.T b/testsuite/tests/patsyn/should_fail/all.T
index 27ebc8bdd4..02cc2cec2c 100644
--- a/testsuite/tests/patsyn/should_fail/all.T
+++ b/testsuite/tests/patsyn/should_fail/all.T
@@ -46,3 +46,4 @@ test('T15685', normal, compile_fail, [''])
 test('T15692', normal, compile, [''])   # It has -fdefer-type-errors inside
 test('T15694', normal, compile_fail, [''])
 test('T16900', normal, compile_fail, ['-fdiagnostics-show-caret'])
+test('T14552', normal, compile_fail, [''])