diff --git a/src/librustc/middle/reachable.rs b/src/librustc/middle/reachable.rs
index d665d279a175..61442e190956 100644
--- a/src/librustc/middle/reachable.rs
+++ b/src/librustc/middle/reachable.rs
@@ -374,7 +374,8 @@ impl ReachableContext {
     // this properly would result in the necessity of computing *type*
     // reachability, which might result in a compile time loss.
     fn mark_destructors_reachable(&self) {
-        for (_, destructor_def_id) in self.tcx.destructor_for_type.iter() {
+        let destructor_for_type = self.tcx.destructor_for_type.borrow();
+        for (_, destructor_def_id) in destructor_for_type.get().iter() {
             if destructor_def_id.crate == ast::LOCAL_CRATE {
                 self.reachable_symbols.insert(destructor_def_id.node);
             }
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 354f0b7ae39f..1d0bc49b8c9d 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -327,7 +327,7 @@ struct ctxt_ {
     // of the method that implements its destructor. If the type is not
     // present in this map, it does not have a destructor. This map is
     // populated during the coherence phase of typechecking.
-    destructor_for_type: @mut HashMap<ast::DefId, ast::DefId>,
+    destructor_for_type: RefCell<HashMap<ast::DefId, ast::DefId>>,
 
     // A method will be in this list if and only if it is a destructor.
     destructors: @mut HashSet<ast::DefId>,
@@ -1003,7 +1003,7 @@ pub fn mk_ctxt(s: session::Session,
         lang_items: lang_items,
         provided_method_sources: RefCell::new(HashMap::new()),
         supertraits: RefCell::new(HashMap::new()),
-        destructor_for_type: @mut HashMap::new(),
+        destructor_for_type: RefCell::new(HashMap::new()),
         destructors: @mut HashSet::new(),
         trait_impls: @mut HashMap::new(),
         inherent_impls:  @mut HashMap::new(),
@@ -3813,7 +3813,8 @@ impl DtorKind {
 /* If struct_id names a struct with a dtor, return Some(the dtor's id).
    Otherwise return none. */
 pub fn ty_dtor(cx: ctxt, struct_id: DefId) -> DtorKind {
-    match cx.destructor_for_type.find(&struct_id) {
+    let destructor_for_type = cx.destructor_for_type.borrow();
+    match destructor_for_type.get().find(&struct_id) {
         Some(&method_def_id) => {
             let flag = !has_attr(cx, struct_id, "unsafe_no_drop_flag");
 
diff --git a/src/librustc/middle/typeck/check/method.rs b/src/librustc/middle/typeck/check/method.rs
index 3838dce9472c..56e9f6be55e6 100644
--- a/src/librustc/middle/typeck/check/method.rs
+++ b/src/librustc/middle/typeck/check/method.rs
@@ -1157,7 +1157,10 @@ impl<'a> LookupContext<'a> {
             // that self has been merged in? -sully
             method_param(method_param { trait_id: trait_id, .. }) |
             method_object(method_object { trait_id: trait_id, .. }) => {
-                bad = self.tcx().destructor_for_type.contains_key(&trait_id);
+                let destructor_for_type = self.tcx()
+                                              .destructor_for_type
+                                              .borrow();
+                bad = destructor_for_type.get().contains_key(&trait_id);
             }
         }
 
diff --git a/src/librustc/middle/typeck/coherence.rs b/src/librustc/middle/typeck/coherence.rs
index 47f4cc5ea152..0371f877f4fa 100644
--- a/src/librustc/middle/typeck/coherence.rs
+++ b/src/librustc/middle/typeck/coherence.rs
@@ -705,8 +705,10 @@ impl CoherenceChecker {
             let self_type = self.get_self_type_for_implementation(*impl_info);
             match ty::get(self_type.ty).sty {
                 ty::ty_struct(type_def_id, _) => {
-                    tcx.destructor_for_type.insert(type_def_id,
-                                                   method_def_id);
+                    let mut destructor_for_type = tcx.destructor_for_type
+                                                     .borrow_mut();
+                    destructor_for_type.get().insert(type_def_id,
+                                                     method_def_id);
                     tcx.destructors.insert(method_def_id);
                 }
                 _ => {