diff --git a/docs/examples/tristate/tristate.sby b/docs/examples/tristate/tristate.sby
index 7970774..f85e937 100644
--- a/docs/examples/tristate/tristate.sby
+++ b/docs/examples/tristate/tristate.sby
@@ -3,6 +3,7 @@ pass
 fail
 
 [options]
+fail: expect fail
 mode prove
 depth 5