diff --git a/components/layout/parallel.rs b/components/layout/parallel.rs
index 322bfa07d2e..efe49165850 100644
--- a/components/layout/parallel.rs
+++ b/components/layout/parallel.rs
@@ -333,8 +333,6 @@ trait ParallelPreorderFlowTraversal : PreorderFlowTraversal {
     }
 }
 
-impl<'a> ParallelPostorderFlowTraversal for BubbleISizes<'a> {}
-
 impl<'a> ParallelPreorderFlowTraversal for AssignISizes<'a> {
     fn run_parallel(&self,
                     unsafe_flows: UnsafeFlowList,