diff --git a/src/librustc/back/link.rs b/src/librustc/back/link.rs
index 11a63db6aba..92586863a85 100644
--- a/src/librustc/back/link.rs
+++ b/src/librustc/back/link.rs
@@ -521,14 +521,18 @@ pub fn symbol_hash(tcx: ty::ctxt,
 }
 
 pub fn get_symbol_hash(ccx: &mut CrateContext, t: ty::t) -> @str {
-    match ccx.type_hashcodes.find(&t) {
-      Some(&h) => h,
-      None => {
-        let hash = symbol_hash(ccx.tcx, &mut ccx.symbol_hasher, t, &ccx.link_meta);
-        ccx.type_hashcodes.insert(t, hash);
-        hash
-      }
+    {
+        let type_hashcodes = ccx.type_hashcodes.borrow();
+        match type_hashcodes.get().find(&t) {
+            Some(&h) => return h,
+            None => {}
+        }
     }
+
+    let mut type_hashcodes = ccx.type_hashcodes.borrow_mut();
+    let hash = symbol_hash(ccx.tcx, &mut ccx.symbol_hasher, t, &ccx.link_meta);
+    type_hashcodes.get().insert(t, hash);
+    hash
 }
 
 
diff --git a/src/librustc/middle/trans/context.rs b/src/librustc/middle/trans/context.rs
index 23e6e897f59..8939894ee38 100644
--- a/src/librustc/middle/trans/context.rs
+++ b/src/librustc/middle/trans/context.rs
@@ -96,7 +96,7 @@ pub struct CrateContext {
      llsizingtypes: RefCell<HashMap<ty::t, Type>>,
      adt_reprs: RefCell<HashMap<ty::t, @adt::Repr>>,
      symbol_hasher: Sha256,
-     type_hashcodes: HashMap<ty::t, @str>,
+     type_hashcodes: RefCell<HashMap<ty::t, @str>>,
      type_short_names: HashMap<ty::t, ~str>,
      all_llvm_symbols: HashSet<@str>,
      tcx: ty::ctxt,
@@ -207,7 +207,7 @@ pub fn new(sess: session::Session,
                   llsizingtypes: RefCell::new(HashMap::new()),
                   adt_reprs: RefCell::new(HashMap::new()),
                   symbol_hasher: symbol_hasher,
-                  type_hashcodes: HashMap::new(),
+                  type_hashcodes: RefCell::new(HashMap::new()),
                   type_short_names: HashMap::new(),
                   all_llvm_symbols: HashSet::new(),
                   tcx: tcx,