diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs
index 4c2dd8c27186..10156d22501e 100644
--- a/src/librustc/diagnostics.rs
+++ b/src/librustc/diagnostics.rs
@@ -2087,7 +2087,7 @@ use std::cell::Cell;
 
 trait Trait<'a> { }
 
-impl Trait<'b> for Cell<&'a u32> { }
+impl<'a, 'b> Trait<'b> for Cell<&'a u32> { }
 
 fn foo<'x, 'y>(x: Cell<&'x u32>) -> impl Trait<'y>
 where 'x: 'y