diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 74f7b37265a..d62a58460d0 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -18,6 +18,7 @@
  */
 
 use driver::session;
+use std::cell::RefCell;
 use std::hashmap::HashMap;
 use syntax::ast;
 use syntax::codemap::Span;
@@ -33,7 +34,7 @@ pub type NamedRegionMap = HashMap<ast::NodeId, ast::DefRegion>;
 
 struct LifetimeContext {
     sess: session::Session,
-    named_region_map: @mut NamedRegionMap,
+    named_region_map: @RefCell<NamedRegionMap>,
 }
 
 enum ScopeChain<'a> {
@@ -43,12 +44,11 @@ enum ScopeChain<'a> {
     RootScope
 }
 
-pub fn crate(sess: session::Session,
-             crate: &ast::Crate)
-             -> @mut NamedRegionMap {
+pub fn crate(sess: session::Session, crate: &ast::Crate)
+             -> @RefCell<NamedRegionMap> {
     let mut ctxt = LifetimeContext {
         sess: sess,
-        named_region_map: @mut HashMap::new()
+        named_region_map: @RefCell::new(HashMap::new())
     };
     visit::walk_crate(&mut ctxt, crate, &RootScope);
     sess.abort_if_errors();
@@ -305,7 +305,8 @@ impl LifetimeContext {
                                 self.sess.intr()),
                 lifetime_ref.id,
                 def);
-        self.named_region_map.insert(lifetime_ref.id, def);
+        let mut named_region_map = self.named_region_map.borrow_mut();
+        named_region_map.get().insert(lifetime_ref.id, def);
     }
 }
 
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index b86fa8ade77..7527a7e9d02 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -270,7 +270,7 @@ struct ctxt_ {
     sess: session::Session,
     def_map: resolve::DefMap,
 
-    named_region_map: @mut resolve_lifetime::NamedRegionMap,
+    named_region_map: @RefCell<resolve_lifetime::NamedRegionMap>,
 
     region_maps: @mut middle::region::RegionMaps,
 
@@ -959,7 +959,7 @@ pub type node_type_table = RefCell<HashMap<uint,t>>;
 
 pub fn mk_ctxt(s: session::Session,
                dm: resolve::DefMap,
-               named_region_map: @mut resolve_lifetime::NamedRegionMap,
+               named_region_map: @RefCell<resolve_lifetime::NamedRegionMap>,
                amap: ast_map::map,
                freevars: freevars::freevar_map,
                region_maps: @mut middle::region::RegionMaps,
diff --git a/src/librustc/middle/typeck/astconv.rs b/src/librustc/middle/typeck/astconv.rs
index 709791689d6..66e49c99b0b 100644
--- a/src/librustc/middle/typeck/astconv.rs
+++ b/src/librustc/middle/typeck/astconv.rs
@@ -76,12 +76,10 @@ pub trait AstConv {
     fn ty_infer(&self, span: Span) -> ty::t;
 }
 
-pub fn ast_region_to_region(
-    tcx: ty::ctxt,
-    lifetime: &ast::Lifetime)
-    -> ty::Region
-{
-    let r = match tcx.named_region_map.find(&lifetime.id) {
+pub fn ast_region_to_region(tcx: ty::ctxt, lifetime: &ast::Lifetime)
+                            -> ty::Region {
+    let named_region_map = tcx.named_region_map.borrow();
+    let r = match named_region_map.get().find(&lifetime.id) {
         None => {
             // should have been recorded by the `resolve_lifetime` pass
             tcx.sess.span_bug(lifetime.span, "unresolved lifetime");