diff --git a/src/librustc_driver/test.rs b/src/librustc_driver/test.rs
index 9efd8844977f..971855ee2d00 100644
--- a/src/librustc_driver/test.rs
+++ b/src/librustc_driver/test.rs
@@ -303,7 +303,7 @@ impl<'a, 'gcx, 'tcx> Env<'a, 'gcx, 'tcx> {
 
     pub fn t_param(&self, index: u32) -> Ty<'tcx> {
         let name = format!("T{}", index);
-        self.infcx.tcx.mk_param(index, Symbol::intern(&name))
+        self.infcx.tcx.mk_param(index, Symbol::intern(&name).as_str())
     }
 
     pub fn re_early_bound(&self, index: u32, name: &'static str) -> ty::Region<'tcx> {