diff --git a/src/librustc/middle/infer/freshen.rs b/src/librustc/middle/infer/freshen.rs
index 02c52f829676..6bc424fdf952 100644
--- a/src/librustc/middle/infer/freshen.rs
+++ b/src/librustc/middle/infer/freshen.rs
@@ -135,10 +135,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
                 t
             }
 
-            ty::ty_open(..) => {
-                self.tcx().sess.bug("Cannot freshen an open existential type");
-            }
-
+            ty::ty_open(..) |
             ty::ty_bool |
             ty::ty_char |
             ty::ty_int(..) |
diff --git a/src/librustc/middle/traits/select.rs b/src/librustc/middle/traits/select.rs
index 25a33de1cc7f..756ddd91782b 100644
--- a/src/librustc/middle/traits/select.rs
+++ b/src/librustc/middle/traits/select.rs
@@ -1457,11 +1457,26 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 Ok(AmbiguousBuiltin)
             }
 
+            ty::ty_open(ty) => {
+                // these only crop up in trans, and represent an
+                // "opened" unsized/existential type (one that has
+                // been dereferenced)
+                match bound {
+                    ty::BoundCopy |
+                    ty::BoundSync |
+                    ty::BoundSend => {
+                        Ok(If(vec!(ty)))
+                    }
+
+                    ty::BoundSized => {
+                        Err(Unimplemented)
+                    }
+                }
+            }
             ty::ty_err => {
                 Ok(If(Vec::new()))
             }
 
-            ty::ty_open(_) |
             ty::ty_infer(ty::FreshTy(_)) |
             ty::ty_infer(ty::FreshIntTy(_)) => {
                 self.tcx().sess.bug(
diff --git a/src/librustc_trans/trans/common.rs b/src/librustc_trans/trans/common.rs
index 237fc1856369..057c6619d726 100644
--- a/src/librustc_trans/trans/common.rs
+++ b/src/librustc_trans/trans/common.rs
@@ -50,7 +50,7 @@ use std::vec::Vec;
 use syntax::ast::Ident;
 use syntax::ast;
 use syntax::ast_map::{PathElem, PathName};
-use syntax::codemap::Span;
+use syntax::codemap::{DUMMY_SP, Span};
 use syntax::parse::token::InternedString;
 use syntax::parse::token;
 use util::common::memoized;
@@ -114,8 +114,9 @@ pub fn normalize_ty<'tcx>(cx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> Ty<'tcx> {
 }
 
 // Is the type's representation size known at compile time?
-pub fn type_is_sized<'tcx>(cx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> bool {
-ty::type_contents(cx, ty).is_sized(cx)
+pub fn type_is_sized<'tcx>(tcx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> bool {
+    let param_env = ty::empty_parameter_environment(tcx);
+    ty::type_is_sized(&param_env, DUMMY_SP, ty)
 }
 
 pub fn lltype_is_sized<'tcx>(cx: &ty::ctxt<'tcx>, ty: Ty<'tcx>) -> bool {