diff --git a/collector/compile-benchmarks/html5ever/build.rs b/collector/compile-benchmarks/html5ever/build.rs
index b01463891..3c30b79c3 100644
--- a/collector/compile-benchmarks/html5ever/build.rs
+++ b/collector/compile-benchmarks/html5ever/build.rs
@@ -7,6 +7,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![allow(soft_unstable)]
+
 extern crate phf_codegen;
 extern crate rustc_serialize;