diff --git a/src/librustc/arena.rs b/src/librustc/arena.rs
index 02ed30dd386..a9b7aa4c10d 100644
--- a/src/librustc/arena.rs
+++ b/src/librustc/arena.rs
@@ -14,7 +14,7 @@ macro_rules! arena_types {
                 rustc::hir::def_id::DefId,
                 rustc::ty::subst::SubstsRef<$tcx>
             )>,
-            [few] mir_keys: rustc::util::nodemap::DefIdSet,
+            [few, decode] mir_keys: rustc::util::nodemap::DefIdSet,
             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
             [] region_scope_tree: rustc::middle::region::ScopeTree,
             [] item_local_set: rustc::util::nodemap::ItemLocalSet,
diff --git a/src/librustc/query/mod.rs b/src/librustc/query/mod.rs
index 4514121da91..44a0cf55079 100644
--- a/src/librustc/query/mod.rs
+++ b/src/librustc/query/mod.rs
@@ -359,7 +359,7 @@ rustc_queries! {
     }
 
     Other {
-        query used_trait_imports(_: DefId) -> Lrc<DefIdSet> {}
+        query used_trait_imports(_: DefId) -> &'tcx DefIdSet {}
     }
 
     TypeChecking {
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index a20a91b3e6f..6ff4fe9eff1 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -808,8 +808,8 @@ fn has_typeck_tables<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn used_trait_imports<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 def_id: DefId)
-                                -> Lrc<DefIdSet> {
-    tcx.typeck_tables_of(def_id).used_trait_imports.clone()
+                                -> &'tcx DefIdSet {
+    &*tcx.typeck_tables_of(def_id).used_trait_imports
 }
 
 fn typeck_tables_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,