diff --git a/docs/users_guide/exts/ffi.rst b/docs/users_guide/exts/ffi.rst
index 2889fb141008f28fb95c423b9c5afb3b1857c0b4..e3bf1a75727ea535059d8df6ff39d785594c04fd 100644
--- a/docs/users_guide/exts/ffi.rst
+++ b/docs/users_guide/exts/ffi.rst
@@ -998,7 +998,7 @@ the data.  We can do it like this:
        sp <- newStablePtrPrimMVar mvar
        fp <- mallocForeignPtr
        withForeignPtr fp $ \presult -> do
-         cap <- threadCapability =<< myThreadId
+         (cap, _) <- threadCapability =<< myThreadId
          scheduleCallback sp cap presult
          takeMVar mvar `onException`
            forkIO (do takeMVar mvar; touchForeignPtr fp)