diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs
index a8955723e3a..b5d2bb1cffc 100644
--- a/src/librustc/middle/mem_categorization.rs
+++ b/src/librustc/middle/mem_categorization.rs
@@ -517,7 +517,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
                     // a bind-by-ref means that the base_ty will be the type of the ident itself,
                     // but what we want here is the type of the underlying value being borrowed.
                     // So peel off one-level, turning the &T into T.
-                    match base_ty.builtin_deref(false, ty::NoPreference) {
+                    match base_ty.builtin_deref(false) {
                         Some(t) => t.ty,
                         None => {
                             debug!("By-ref binding of non-derefable type {:?}", base_ty);
@@ -1019,7 +1019,7 @@ impl<'a, 'gcx, 'tcx> MemCategorizationContext<'a, 'gcx, 'tcx> {
         debug!("cat_deref: base_cmt={:?}", base_cmt);
 
         let base_cmt_ty = base_cmt.ty;
-        let deref_ty = match base_cmt_ty.builtin_deref(true, ty::NoPreference) {
+        let deref_ty = match base_cmt_ty.builtin_deref(true) {
             Some(mt) => mt.ty,
             None => {
                 debug!("Explicit deref of non-derefable type: {:?}",
diff --git a/src/librustc/mir/tcx.rs b/src/librustc/mir/tcx.rs
index 23f360d5c39..53607764b39 100644
--- a/src/librustc/mir/tcx.rs
+++ b/src/librustc/mir/tcx.rs
@@ -52,7 +52,7 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
         match *elem {
             ProjectionElem::Deref => {
                 let ty = self.to_ty(tcx)
-                             .builtin_deref(true, ty::LvaluePreference::NoPreference)
+                             .builtin_deref(true)
                              .unwrap_or_else(|| {
                                  bug!("deref projection of non-dereferencable ty {:?}", self)
                              })
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 63df1179af2..600c823aaf8 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -12,7 +12,6 @@ pub use self::Variance::*;
 pub use self::AssociatedItemContainer::*;
 pub use self::BorrowKind::*;
 pub use self::IntVarValue::*;
-pub use self::LvaluePreference::*;
 pub use self::fold::TypeFoldable;
 
 use hir::{map as hir_map, FreevarMap, TraitMap};
@@ -2099,21 +2098,6 @@ impl<'tcx> TyS<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum LvaluePreference {
-    PreferMutLvalue,
-    NoPreference
-}
-
-impl LvaluePreference {
-    pub fn from_mutbl(m: hir::Mutability) -> Self {
-        match m {
-            hir::MutMutable => PreferMutLvalue,
-            hir::MutImmutable => NoPreference,
-        }
-    }
-}
-
 impl BorrowKind {
     pub fn from_mutbl(m: hir::Mutability) -> BorrowKind {
         match m {
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index db7e4fe45ef..0c1ebd1a2ba 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -1514,18 +1514,12 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
     ///
     /// The parameter `explicit` indicates if this is an *explicit* dereference.
     /// Some types---notably unsafe ptrs---can only be dereferenced explicitly.
-    pub fn builtin_deref(&self, explicit: bool, pref: ty::LvaluePreference)
-        -> Option<TypeAndMut<'tcx>>
-    {
+    pub fn builtin_deref(&self, explicit: bool) -> Option<TypeAndMut<'tcx>> {
         match self.sty {
             TyAdt(def, _) if def.is_box() => {
                 Some(TypeAndMut {
                     ty: self.boxed_ty(),
-                    mutbl: if pref == ty::PreferMutLvalue {
-                        hir::MutMutable
-                    } else {
-                        hir::MutImmutable
-                    },
+                    mutbl: hir::MutImmutable,
                 })
             },
             TyRef(_, mt) => Some(mt),
diff --git a/src/librustc_mir/borrow_check/nll/type_check/mod.rs b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
index 9dcd4435580..6d9354360d3 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/mod.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/mod.rs
@@ -397,7 +397,7 @@ impl<'a, 'b, 'gcx, 'tcx> TypeVerifier<'a, 'b, 'gcx, 'tcx> {
         let base_ty = base.to_ty(tcx);
         match *pi {
             ProjectionElem::Deref => {
-                let deref_ty = base_ty.builtin_deref(true, ty::LvaluePreference::NoPreference);
+                let deref_ty = base_ty.builtin_deref(true);
                 PlaceTy::Ty {
                     ty: deref_ty.map(|t| t.ty).unwrap_or_else(|| {
                         span_mirbug_and_err!(self, place, "deref of non-pointer {:?}", base_ty)
diff --git a/src/librustc_trans/abi.rs b/src/librustc_trans/abi.rs
index 9cabd9356e9..4c17929fe98 100644
--- a/src/librustc_trans/abi.rs
+++ b/src/librustc_trans/abi.rs
@@ -674,7 +674,7 @@ impl<'a, 'tcx> FnType<'tcx> {
                 _ => bug!("FnType::new_vtable: non-pair self {:?}", self_arg)
             }
 
-            let pointee = self_arg.layout.ty.builtin_deref(true, ty::NoPreference)
+            let pointee = self_arg.layout.ty.builtin_deref(true)
                 .unwrap_or_else(|| {
                     bug!("FnType::new_vtable: non-pointer self {:?}", self_arg)
                 }).ty;
diff --git a/src/librustc_trans/mir/constant.rs b/src/librustc_trans/mir/constant.rs
index 71ce0aa3da9..b4cdf38a513 100644
--- a/src/librustc_trans/mir/constant.rs
+++ b/src/librustc_trans/mir/constant.rs
@@ -740,7 +740,7 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
                         operand.llval
                     }
                     mir::CastKind::Unsize => {
-                        let pointee_ty = operand.ty.builtin_deref(true, ty::NoPreference)
+                        let pointee_ty = operand.ty.builtin_deref(true)
                             .expect("consts: unsizing got non-pointer type").ty;
                         let (base, old_info) = if !self.cx.type_is_sized(pointee_ty) {
                             // Normally, the source is a thin pointer and we are
@@ -755,7 +755,7 @@ impl<'a, 'tcx> MirConstContext<'a, 'tcx> {
                             (operand.llval, None)
                         };
 
-                        let unsized_ty = cast_ty.builtin_deref(true, ty::NoPreference)
+                        let unsized_ty = cast_ty.builtin_deref(true)
                             .expect("consts: unsizing got non-pointer target type").ty;
                         let ptr_ty = self.cx.layout_of(unsized_ty).llvm_type(self.cx).ptr_to();
                         let base = consts::ptrcast(base, ptr_ty);
diff --git a/src/librustc_trans/mir/operand.rs b/src/librustc_trans/mir/operand.rs
index 25db9f9b4c8..e1b906646aa 100644
--- a/src/librustc_trans/mir/operand.rs
+++ b/src/librustc_trans/mir/operand.rs
@@ -9,7 +9,6 @@
 // except according to those terms.
 
 use llvm::ValueRef;
-use rustc::ty;
 use rustc::ty::layout::{self, Align, LayoutOf, TyLayout};
 use rustc::mir;
 use rustc_data_structures::indexed_vec::Idx;
@@ -100,7 +99,7 @@ impl<'a, 'tcx> OperandRef<'tcx> {
     }
 
     pub fn deref(self, cx: &CodegenCx<'a, 'tcx>) -> PlaceRef<'tcx> {
-        let projected_ty = self.layout.ty.builtin_deref(true, ty::NoPreference)
+        let projected_ty = self.layout.ty.builtin_deref(true)
             .unwrap_or_else(|| bug!("deref of non-pointer {:?}", self)).ty;
         let (llptr, llextra) = match self.val {
             OperandValue::Immediate(llptr) => (llptr, ptr::null_mut()),
diff --git a/src/librustc_typeck/check/_match.rs b/src/librustc_typeck/check/_match.rs
index d5e4aa69c5b..a6530aa3e15 100644
--- a/src/librustc_typeck/check/_match.rs
+++ b/src/librustc_typeck/check/_match.rs
@@ -14,8 +14,8 @@ use rustc::hir::pat_util::EnumerateAndAdjustIterator;
 use rustc::infer;
 use rustc::infer::type_variable::TypeVariableOrigin;
 use rustc::traits::ObligationCauseCode;
-use rustc::ty::{self, Ty, TypeFoldable, LvaluePreference};
-use check::{FnCtxt, Expectation, Diverges};
+use rustc::ty::{self, Ty, TypeFoldable};
+use check::{FnCtxt, Expectation, Diverges, LvaluePreference};
 use check::coercion::CoerceMany;
 use util::nodemap::FxHashMap;
 
@@ -500,7 +500,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
 
     pub fn check_dereferencable(&self, span: Span, expected: Ty<'tcx>, inner: &hir::Pat) -> bool {
         if let PatKind::Binding(..) = inner.node {
-            if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true, ty::NoPreference) {
+            if let Some(mt) = self.shallow_resolve(expected).builtin_deref(true) {
                 if let ty::TyDynamic(..) = mt.ty.sty {
                     // This is "x = SomeTrait" being reduced from
                     // "let &x = &SomeTrait" or "let box x = Box<SomeTrait>", an error.
diff --git a/src/librustc_typeck/check/autoderef.rs b/src/librustc_typeck/check/autoderef.rs
index 169959d12b5..fec9f4c658e 100644
--- a/src/librustc_typeck/check/autoderef.rs
+++ b/src/librustc_typeck/check/autoderef.rs
@@ -10,7 +10,7 @@
 
 use astconv::AstConv;
 
-use super::{FnCtxt, LvalueOp};
+use super::{FnCtxt, LvalueOp, LvaluePreference};
 use super::method::MethodCallee;
 
 use rustc::infer::InferOk;
@@ -18,7 +18,6 @@ use rustc::session::DiagnosticMessageId;
 use rustc::traits;
 use rustc::ty::{self, Ty, TraitRef};
 use rustc::ty::{ToPredicate, TypeFoldable};
-use rustc::ty::{LvaluePreference, NoPreference};
 use rustc::ty::adjustment::{Adjustment, Adjust, OverloadedDeref};
 
 use syntax_pos::Span;
@@ -85,7 +84,7 @@ impl<'a, 'gcx, 'tcx> Iterator for Autoderef<'a, 'gcx, 'tcx> {
 
         // Otherwise, deref if type is derefable:
         let (kind, new_ty) =
-            if let Some(mt) = self.cur_ty.builtin_deref(self.include_raw_pointers, NoPreference) {
+            if let Some(mt) = self.cur_ty.builtin_deref(self.include_raw_pointers) {
                 (AutoderefKind::Builtin, mt.ty)
             } else {
                 let ty = self.overloaded_deref_ty(self.cur_ty)?;
@@ -238,8 +237,8 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
     pub fn try_overloaded_deref(&self,
                                 span: Span,
                                 base_ty: Ty<'tcx>,
-                                pref: LvaluePreference)
+                                needs: Needs)
                                 -> Option<InferOk<'tcx, MethodCallee<'tcx>>> {
-        self.try_overloaded_lvalue_op(span, base_ty, &[], pref, LvalueOp::Deref)
+        self.try_overloaded_lvalue_op(span, base_ty, &[], needs, LvalueOp::Deref)
     }
 }
diff --git a/src/librustc_typeck/check/callee.rs b/src/librustc_typeck/check/callee.rs
index 5c5e5f2735b..84e1de5c362 100644
--- a/src/librustc_typeck/check/callee.rs
+++ b/src/librustc_typeck/check/callee.rs
@@ -8,14 +8,14 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use super::{Expectation, FnCtxt, TupleArgumentsFlag};
+use super::{Expectation, FnCtxt, LvaluePreference, TupleArgumentsFlag};
 use super::autoderef::Autoderef;
 use super::method::MethodCallee;
 
 use hir::def::Def;
 use hir::def_id::{DefId, LOCAL_CRATE};
 use rustc::{infer, traits};
-use rustc::ty::{self, TyCtxt, TypeFoldable, LvaluePreference, Ty};
+use rustc::ty::{self, TyCtxt, TypeFoldable, Ty};
 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
 use syntax::abi;
 use syntax::symbol::Symbol;
diff --git a/src/librustc_typeck/check/coercion.rs b/src/librustc_typeck/check/coercion.rs
index edda557c98c..25c175c5388 100644
--- a/src/librustc_typeck/check/coercion.rs
+++ b/src/librustc_typeck/check/coercion.rs
@@ -60,7 +60,7 @@
 //! sort of a minor point so I've opted to leave it for later---after all
 //! we may want to adjust precisely when coercions occur.
 
-use check::{Diverges, FnCtxt};
+use check::{Diverges, FnCtxt, LvaluePreference};
 
 use rustc::hir;
 use rustc::hir::def_id::DefId;
@@ -69,8 +69,7 @@ use rustc::infer::type_variable::TypeVariableOrigin;
 use rustc::lint;
 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
-use rustc::ty::{self, LvaluePreference, TypeAndMut,
-                Ty, ClosureSubsts};
+use rustc::ty::{self, TypeAndMut, Ty, ClosureSubsts};
 use rustc::ty::fold::TypeFoldable;
 use rustc::ty::error::TypeError;
 use rustc::ty::relate::RelateResult;
diff --git a/src/librustc_typeck/check/method/confirm.rs b/src/librustc_typeck/check/method/confirm.rs
index 3a9c4e1901d..3f4281d2a60 100644
--- a/src/librustc_typeck/check/method/confirm.rs
+++ b/src/librustc_typeck/check/method/confirm.rs
@@ -11,11 +11,11 @@
 use super::{probe, MethodCallee};
 
 use astconv::AstConv;
-use check::{FnCtxt, LvalueOp, callee};
+use check::{FnCtxt, LvalueOp, callee, LvaluePreference, PreferMutLvalue};
 use hir::def_id::DefId;
 use rustc::ty::subst::Substs;
 use rustc::traits;
-use rustc::ty::{self, LvaluePreference, NoPreference, PreferMutLvalue, Ty};
+use rustc::ty::{self, Ty};
 use rustc::ty::subst::Subst;
 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, OverloadedDeref};
 use rustc::ty::fold::TypeFoldable;
@@ -500,7 +500,7 @@ impl<'a, 'gcx, 'tcx> ConfirmContext<'a, 'gcx, 'tcx> {
         let base_ty = self.resolve_type_vars_if_possible(&base_ty);
 
         // Need to deref because overloaded lvalue ops take self by-reference.
-        let base_ty = base_ty.builtin_deref(false, NoPreference)
+        let base_ty = base_ty.builtin_deref(false)
             .expect("lvalue op takes something that is not a ref")
             .ty;
 
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 9b24c09036b..4514910f1b5 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -77,6 +77,7 @@ type parameter).
 */
 
 pub use self::Expectation::*;
+use self::LvaluePreference::*;
 use self::autoderef::Autoderef;
 use self::callee::DeferredCallResolution;
 use self::coercion::{CoerceMany, DynamicCoerceMany};
@@ -95,7 +96,6 @@ use rustc::infer::type_variable::{TypeVariableOrigin};
 use rustc::middle::region;
 use rustc::ty::subst::{Kind, Subst, Substs};
 use rustc::traits::{self, FulfillmentContext, ObligationCause, ObligationCauseCode};
-use rustc::ty::{ParamTy, LvaluePreference, NoPreference, PreferMutLvalue};
 use rustc::ty::{self, Ty, TyCtxt, Visibility, ToPredicate};
 use rustc::ty::adjustment::{Adjust, Adjustment, AutoBorrow};
 use rustc::ty::fold::TypeFoldable;
@@ -368,6 +368,21 @@ impl<'a, 'gcx, 'tcx> Expectation<'tcx> {
     }
 }
 
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum LvaluePreference {
+    PreferMutLvalue,
+    NoPreference
+}
+
+impl LvaluePreference {
+    fn from_mutbl(m: hir::Mutability) -> Self {
+        match m {
+            hir::MutMutable => PreferMutLvalue,
+            hir::MutImmutable => NoPreference,
+        }
+    }
+}
+
 #[derive(Copy, Clone)]
 pub struct UnsafetyState {
     pub def: ast::NodeId,
@@ -2219,7 +2234,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
         let ret_ty = method.sig.output();
 
         // method returns &T, but the type as visible to user is T, so deref
-        ret_ty.builtin_deref(true, NoPreference).unwrap()
+        ret_ty.builtin_deref(true).unwrap()
     }
 
     fn lookup_indexing(&self,
@@ -3572,7 +3587,7 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                 oprnd_t = self.structurally_resolved_type(expr.span, oprnd_t);
                 match unop {
                     hir::UnDeref => {
-                        if let Some(mt) = oprnd_t.builtin_deref(true, NoPreference) {
+                        if let Some(mt) = oprnd_t.builtin_deref(true) {
                             oprnd_t = mt.ty;
                         } else if let Some(ok) = self.try_overloaded_deref(
                                 expr.span, oprnd_t, lvalue_pref) {
@@ -5023,7 +5038,7 @@ pub fn check_bounds_are_used<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let lifetime_count = generics.lifetimes().count();
 
     for leaf_ty in ty.walk() {
-        if let ty::TyParam(ParamTy {idx, ..}) = leaf_ty.sty {
+        if let ty::TyParam(ty::ParamTy {idx, ..}) = leaf_ty.sty {
             debug!("Found use of ty param num {}", idx);
             tps_used[idx as usize - lifetime_count] = true;
         } else if let ty::TyError = leaf_ty.sty {
diff --git a/src/librustc_typeck/check/op.rs b/src/librustc_typeck/check/op.rs
index e099d1c0c25..0d02212e725 100644
--- a/src/librustc_typeck/check/op.rs
+++ b/src/librustc_typeck/check/op.rs
@@ -10,9 +10,9 @@
 
 //! Code related to processing overloaded binary and unary operators.
 
-use super::FnCtxt;
+use super::{FnCtxt, NoPreference, PreferMutLvalue};
 use super::method::MethodCallee;
-use rustc::ty::{self, Ty, TypeFoldable, NoPreference, PreferMutLvalue, TypeVariants};
+use rustc::ty::{self, Ty, TypeFoldable, TypeVariants};
 use rustc::ty::TypeVariants::{TyStr, TyRef};
 use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
 use rustc::infer::type_variable::TypeVariableOrigin;