diff --git a/src/librustc/middle/trans/_match.rs b/src/librustc/middle/trans/_match.rs
index 9f2b6833374e..75db7518f54b 100644
--- a/src/librustc/middle/trans/_match.rs
+++ b/src/librustc/middle/trans/_match.rs
@@ -1358,8 +1358,6 @@ fn insert_lllocals(bcx: @Block,
      * the bindings.
      */
 
-    let llmap = bcx.fcx.lllocals;
-
     for (&ident, &binding_info) in bindings_map.iter() {
         let llval = match binding_info.trmode {
             // By value bindings: use the stack slot that we
@@ -1378,8 +1376,13 @@ fn insert_lllocals(bcx: @Block,
             }
         };
 
-        debug!("binding {:?} to {}", binding_info.id, bcx.val_to_str(llval));
-        llmap.insert(binding_info.id, llval);
+        {
+            debug!("binding {:?} to {}",
+                   binding_info.id,
+                   bcx.val_to_str(llval));
+            let mut llmap = bcx.fcx.lllocals.borrow_mut();
+            llmap.get().insert(binding_info.id, llval);
+        }
 
         if bcx.sess().opts.extra_debuginfo {
             debuginfo::create_match_binding_metadata(bcx,
@@ -1442,7 +1445,8 @@ fn compile_guard(bcx: @Block,
                 }
                 TrByRef => {}
             }
-            bcx.fcx.lllocals.remove(&binding_info.id);
+            let mut lllocals = bcx.fcx.lllocals.borrow_mut();
+            lllocals.get().remove(&binding_info.id);
         }
         return bcx;
     }
@@ -2057,7 +2061,8 @@ pub fn store_arg(mut bcx: @Block,
         // Optimized path for `x: T` case. This just adopts
         // `llval` wholesale as the pointer for `x`, avoiding the
         // general logic which may copy out of `llval`.
-        bcx.fcx.llargs.insert(pat.id, llval);
+        let mut llargs = bcx.fcx.llargs.borrow_mut();
+        llargs.get().insert(pat.id, llval);
     } else {
         // General path. Copy out the values that are used in the
         // pattern.
@@ -2077,11 +2082,11 @@ fn mk_binding_alloca(mut bcx: @Block,
     let ident = ast_util::path_to_ident(path);
     let llval = alloc_ty(bcx, var_ty, bcx.ident(ident));
     bcx = populate(bcx, var_ty, llval);
-    let llmap = match binding_mode {
-        BindLocal => bcx.fcx.lllocals,
-        BindArgument => bcx.fcx.llargs
+    let mut llmap = match binding_mode {
+        BindLocal => bcx.fcx.lllocals.borrow_mut(),
+        BindArgument => bcx.fcx.llargs.borrow_mut(),
     };
-    llmap.insert(p_id, llval);
+    llmap.get().insert(p_id, llval);
     add_clean(bcx, llval, var_ty);
     return bcx;
 }
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index e02e8e4682b5..dfd5743201cf 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -1692,8 +1692,8 @@ pub fn new_fn_ctxt_w_id(ccx: @CrateContext,
           llself: None,
           personality: None,
           caller_expects_out_pointer: uses_outptr,
-          llargs: @mut HashMap::new(),
-          lllocals: @mut HashMap::new(),
+          llargs: RefCell::new(HashMap::new()),
+          lllocals: RefCell::new(HashMap::new()),
           llupvars: RefCell::new(HashMap::new()),
           id: id,
           param_substs: param_substs,
@@ -2146,7 +2146,10 @@ pub fn trans_enum_variant_or_tuple_like_struct<A:IdAndTy>(
                                              fcx.llretptr.unwrap(),
                                              disr,
                                              i);
-        let llarg = fcx.llargs.get_copy(&fn_arg.pat.id);
+        let llarg = {
+            let llargs = fcx.llargs.borrow();
+            llargs.get().get_copy(&fn_arg.pat.id)
+        };
         let arg_ty = arg_tys[i];
         memcpy_ty(bcx, lldestptr, llarg, arg_ty);
     }
diff --git a/src/librustc/middle/trans/common.rs b/src/librustc/middle/trans/common.rs
index d08917d0db03..bc5c9f8500f7 100644
--- a/src/librustc/middle/trans/common.rs
+++ b/src/librustc/middle/trans/common.rs
@@ -240,10 +240,10 @@ pub struct FunctionContext {
     caller_expects_out_pointer: bool,
 
     // Maps arguments to allocas created for them in llallocas.
-    llargs: @mut HashMap<ast::NodeId, ValueRef>,
+    llargs: RefCell<HashMap<ast::NodeId, ValueRef>>,
     // Maps the def_ids for local variables to the allocas created for
     // them in llallocas.
-    lllocals: @mut HashMap<ast::NodeId, ValueRef>,
+    lllocals: RefCell<HashMap<ast::NodeId, ValueRef>>,
     // Same as above, but for closure upvars
     llupvars: RefCell<HashMap<ast::NodeId, ValueRef>>,
 
diff --git a/src/librustc/middle/trans/debuginfo.rs b/src/librustc/middle/trans/debuginfo.rs
index 14ce27f3bbe4..c1b47488f2ee 100644
--- a/src/librustc/middle/trans/debuginfo.rs
+++ b/src/librustc/middle/trans/debuginfo.rs
@@ -298,11 +298,15 @@ pub fn create_local_var_metadata(bcx: @Block,
         let var_ident = ast_util::path_to_ident(path_ref);
         let var_type = node_id_type(bcx, node_id);
 
-        let llptr = match bcx.fcx.lllocals.find_copy(&node_id) {
-            Some(v) => v,
-            None => {
-                bcx.tcx().sess.span_bug(span,
-                    format!("No entry in lllocals table for {:?}", node_id));
+        let llptr = {
+            let lllocals = bcx.fcx.lllocals.borrow();
+            match lllocals.get().find_copy(&node_id) {
+                Some(v) => v,
+                None => {
+                    bcx.tcx().sess.span_bug(span,
+                        format!("No entry in lllocals table for {:?}",
+                                node_id));
+                }
             }
         };
 
@@ -397,10 +401,17 @@ pub fn create_match_binding_metadata(bcx: @Block,
         return;
     }
 
-    let llptr = match bcx.fcx.lllocals.find_copy(&node_id) {
-        Some(v) => v,
-        None => {
-            bcx.tcx().sess.span_bug(span, format!("No entry in lllocals table for {:?}", node_id));
+    let llptr = {
+        let lllocals = bcx.fcx.lllocals.borrow();
+        match lllocals.get().find_copy(&node_id) {
+            Some(v) => v,
+            None => {
+                bcx.tcx()
+                   .sess
+                   .span_bug(span,
+                             format!("No entry in lllocals table for {:?}",
+                                     node_id));
+            }
         }
     };
 
@@ -506,11 +517,15 @@ pub fn create_argument_metadata(bcx: @Block,
     let scope_metadata = bcx.fcx.debug_context.get_ref(cx, arg.pat.span).fn_metadata;
 
     pat_util::pat_bindings(def_map, arg.pat, |_, node_id, span, path_ref| {
-        let llptr = match bcx.fcx.llargs.find_copy(&node_id) {
-            Some(v) => v,
-            None => {
-                bcx.tcx().sess.span_bug(span,
-                    format!("No entry in llargs table for {:?}", node_id));
+        let llptr = {
+            let llargs = bcx.fcx.llargs.borrow();
+            match llargs.get().find_copy(&node_id) {
+                Some(v) => v,
+                None => {
+                    bcx.tcx().sess.span_bug(span,
+                        format!("No entry in llargs table for {:?}",
+                                node_id));
+                }
             }
         };
 
diff --git a/src/librustc/middle/trans/expr.rs b/src/librustc/middle/trans/expr.rs
index cb3c8f408249..fb68303a4bce 100644
--- a/src/librustc/middle/trans/expr.rs
+++ b/src/librustc/middle/trans/expr.rs
@@ -1100,10 +1100,12 @@ pub fn trans_local_var(bcx: @Block, def: ast::Def) -> Datum {
             }
         }
         ast::DefArg(nid, _) => {
-            take_local(bcx, bcx.fcx.llargs, nid)
+            let llargs = bcx.fcx.llargs.borrow();
+            take_local(bcx, llargs.get(), nid)
         }
         ast::DefLocal(nid, _) | ast::DefBinding(nid, _) => {
-            take_local(bcx, bcx.fcx.lllocals, nid)
+            let lllocals = bcx.fcx.lllocals.borrow();
+            take_local(bcx, lllocals.get(), nid)
         }
         ast::DefSelf(nid, _) => {
             let self_info: ValSelfData = match bcx.fcx.llself {