3 files changed, 34 insertions, 1 deletions
diff --git a/testsuite/tests/typecheck/should_fail/T12406.hs b/testsuite/tests/typecheck/should_fail/T12406.hs
new file mode 100644
index 0000000000..20264cc51d
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T12406.hs
@@ -0,0 +1,20 @@
+{-# LANGUAGE TypeFamilies #-}
+{-# OPTIONS_GHC -fdefer-typed-holes #-}
+
+module T12406 where
+
+-- import Control.Monad  -- comment this out to cause error
+import Data.IORef
+
+class MonadRef m where
+    type Ref m :: * -> *
+    newRef :: a -> m (Ref m a)
+    readRef :: Ref m a -> m a
+
+instance MonadRef IO where
+    type Ref IO = IORef
+    newRef = newIORef
+    readRef = readIORef
+
+foo :: IO ()
+foo = newRef (pure ()) >>= join . readRef
diff --git a/testsuite/tests/typecheck/should_fail/T12406.stderr b/testsuite/tests/typecheck/should_fail/T12406.stderr
new file mode 100644
index 0000000000..85096e6184
--- /dev/null
+++ b/testsuite/tests/typecheck/should_fail/T12406.stderr
@@ -0,0 +1,12 @@
+
+T12406.hs:20:7: error:
+    • Couldn't match type ‘Ref m0’ with ‘IORef’
+      Expected type: IO (Ref m0 (f0 ()))
+        Actual type: IO (Ref IO (f0 ()))
+      The type variable ‘m0’ is ambiguous
+    • In the first argument of ‘(>>=)’, namely ‘newRef (pure ())’
+      In the expression: newRef (pure ()) >>= join . readRef
+      In an equation for ‘foo’: foo = newRef (pure ()) >>= join . readRef
+
+T12406.hs:20:28: error:
+    Variable not in scope: join :: m0 (f0 ()) -> IO ()
diff --git a/testsuite/tests/typecheck/should_fail/all.T b/testsuite/tests/typecheck/should_fail/all.T
index acc3f9f8e9..b064c56a01 100644
--- a/testsuite/tests/typecheck/should_fail/all.T
+++ b/testsuite/tests/typecheck/should_fail/all.T
@@ -423,4 +423,5 @@ test('T12063', [ expect_broken(12063), extra_clean(['T12063.hi-boot', 'T12063.o-
 test('T11974b', normal, compile_fail, [''])
 test('T12151', normal, compile_fail, [''])
 test('T7437', normal, compile_fail, [''])
-test('T12177', normal, compile_fail, [''])
-\ No newline at end of file
+test('T12177', normal, compile_fail, [''])
+test('T12406', normal, compile_fail, [''])