diff --git a/src/doc/unstable-book/src/language-features/optin-builtin-traits.md b/src/doc/unstable-book/src/language-features/optin-builtin-traits.md
index ee24dd87d90c..97b57c690fcc 100644
--- a/src/doc/unstable-book/src/language-features/optin-builtin-traits.md
+++ b/src/doc/unstable-book/src/language-features/optin-builtin-traits.md
@@ -24,9 +24,7 @@ Example:
 ```rust
 #![feature(optin_builtin_traits)]
 
-trait Valid {}
-
-impl Valid for .. {}
+auto trait Valid {}
 
 struct True;
 struct False;
diff --git a/src/librustc_typeck/diagnostics.rs b/src/librustc_typeck/diagnostics.rs
index 33a0c2c34a34..013eb9c8ed2d 100644
--- a/src/librustc_typeck/diagnostics.rs
+++ b/src/librustc_typeck/diagnostics.rs
@@ -1854,7 +1854,7 @@ unsafe impl !Clone for Foo { }
 
 This will compile:
 
-```
+```ignore (ignore auto_trait future compatibility warning)
 #![feature(optin_builtin_traits)]
 
 struct Foo;