diff --git a/src/librustc/ich/impls_ty.rs b/src/librustc/ich/impls_ty.rs
index 3bbac8d6a6425..b43c516f317f2 100644
--- a/src/librustc/ich/impls_ty.rs
+++ b/src/librustc/ich/impls_ty.rs
@@ -181,7 +181,7 @@ impl<'a, 'tcx, A, B> HashStable<StableHashingContext<'a, 'tcx>> for ty::Outlives
 }
 
 impl_stable_hash_for!(struct ty::ProjectionPredicate<'tcx> { projection_ty, ty });
-impl_stable_hash_for!(struct ty::ProjectionTy<'tcx> { trait_ref, item_name });
+impl_stable_hash_for!(struct ty::ProjectionTy<'tcx> { trait_ref, item_def_id });
 
 
 impl<'a, 'tcx> HashStable<StableHashingContext<'a, 'tcx>> for ty::Predicate<'tcx> {
diff --git a/src/librustc/infer/region_inference/mod.rs b/src/librustc/infer/region_inference/mod.rs
index 2e3c2443544f6..acc1a397b4560 100644
--- a/src/librustc/infer/region_inference/mod.rs
+++ b/src/librustc/infer/region_inference/mod.rs
@@ -1542,7 +1542,8 @@ impl<'a, 'gcx, 'tcx> GenericKind<'tcx> {
     pub fn to_ty(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Ty<'tcx> {
         match *self {
             GenericKind::Param(ref p) => p.to_ty(tcx),
-            GenericKind::Projection(ref p) => tcx.mk_projection(p.trait_ref.clone(), p.item_name),
+            GenericKind::Projection(ref p) => tcx.mk_projection(
+                p.trait_ref.clone(), p.item_name(tcx)),
         }
     }
 }
diff --git a/src/librustc/traits/project.rs b/src/librustc/traits/project.rs
index d7911870f391a..f5672ffbdc534 100644
--- a/src/librustc/traits/project.rs
+++ b/src/librustc/traits/project.rs
@@ -355,7 +355,7 @@ pub fn normalize_projection_type<'a, 'b, 'gcx, 'tcx>(
 
             let tcx = selcx.infcx().tcx;
             let def_id = tcx.associated_items(projection_ty.trait_ref.def_id).find(|i|
-                i.name == projection_ty.item_name && i.kind == ty::AssociatedKind::Type
+                i.name == projection_ty.item_name(tcx) && i.kind == ty::AssociatedKind::Type
             ).map(|i| i.def_id).unwrap();
             let ty_var = selcx.infcx().next_ty_var(
                 TypeVariableOrigin::NormalizeProjectionType(tcx.def_span(def_id)));
@@ -436,7 +436,7 @@ fn opt_normalize_projection_type<'a, 'b, 'gcx, 'tcx>(
             //
             // ```
             // let ty = selcx.tcx().mk_projection(projection_ty.trait_ref,
-            //                                    projection_ty.item_name);
+            //                                    projection_ty.item_name(tcx);
             // return Some(NormalizedTy { value: v, obligations: vec![] });
             // ```
 
@@ -574,7 +574,7 @@ fn normalize_to_error<'a, 'gcx, 'tcx>(selcx: &mut SelectionContext<'a, 'gcx, 'tc
                                         predicate: trait_ref.to_predicate() };
     let tcx = selcx.infcx().tcx;
     let def_id = tcx.associated_items(projection_ty.trait_ref.def_id).find(|i|
-        i.name == projection_ty.item_name && i.kind == ty::AssociatedKind::Type
+        i.name == projection_ty.item_name(tcx) && i.kind == ty::AssociatedKind::Type
     ).map(|i| i.def_id).unwrap();
     let new_value = selcx.infcx().next_ty_var(
         TypeVariableOrigin::NormalizeProjectionType(tcx.def_span(def_id)));
@@ -729,7 +729,7 @@ fn project_type<'cx, 'gcx, 'tcx>(
             Ok(ProjectedTy::NoProgress(
                 selcx.tcx().mk_projection(
                     obligation.predicate.trait_ref.clone(),
-                    obligation.predicate.item_name)))
+                    obligation.predicate.item_name(selcx.tcx()))))
         }
     }
 }
@@ -815,7 +815,8 @@ fn assemble_candidates_from_predicates<'cx, 'gcx, 'tcx, I>(
                predicate);
         match predicate {
             ty::Predicate::Projection(ref data) => {
-                let same_name = data.item_name() == obligation.predicate.item_name;
+                let tcx = selcx.tcx();
+                let same_name = data.item_name(tcx) == obligation.predicate.item_name(tcx);
 
                 let is_match = same_name && infcx.probe(|_| {
                     let data_poly_trait_ref =
@@ -902,7 +903,7 @@ fn assemble_candidates_from_impls<'cx, 'gcx, 'tcx>(
                 // type.
                 let node_item = assoc_ty_def(selcx,
                                              impl_data.impl_def_id,
-                                             obligation.predicate.item_name);
+                                             obligation.predicate.item_name(selcx.tcx()));
 
                 let is_default = if node_item.node.is_from_trait() {
                     // If true, the impl inherited a `type Foo = Bar`
@@ -1075,9 +1076,10 @@ fn confirm_object_candidate<'cx, 'gcx, 'tcx>(
 
         // select only those projections that are actually projecting an
         // item with the correct name
+        let tcx = selcx.tcx();
         let env_predicates = env_predicates.filter_map(|p| match p {
             ty::Predicate::Projection(data) =>
-                if data.item_name() == obligation.predicate.item_name {
+                if data.item_name(tcx) == obligation.predicate.item_name(tcx) {
                     Some(data)
                 } else {
                     None
@@ -1180,10 +1182,11 @@ fn confirm_callable_candidate<'cx, 'gcx, 'tcx>(
                                               flag);
 
     let predicate = ty::Binder(ty::ProjectionPredicate { // (1) recreate binder here
-        projection_ty: ty::ProjectionTy {
-            trait_ref: trait_ref,
-            item_name: Symbol::intern(FN_OUTPUT_NAME),
-        },
+        projection_ty: ty::ProjectionTy::from_ref_and_name(
+            tcx,
+            trait_ref,
+            Symbol::intern(FN_OUTPUT_NAME),
+        ),
         ty: ret_type
     });
 
@@ -1228,7 +1231,7 @@ fn confirm_impl_candidate<'cx, 'gcx, 'tcx>(
     let VtableImplData { substs, nested, impl_def_id } = impl_vtable;
 
     let tcx = selcx.tcx();
-    let assoc_ty = assoc_ty_def(selcx, impl_def_id, obligation.predicate.item_name);
+    let assoc_ty = assoc_ty_def(selcx, impl_def_id, obligation.predicate.item_name(tcx));
 
     let ty = if !assoc_ty.item.defaultness.has_value() {
         // This means that the impl is missing a definition for the
diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index e3d7aeb22e1fa..8c801c6fa2b97 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -1323,7 +1323,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                          item_name: Name)
         -> Ty<'tcx> {
             // take a copy of substs so that we own the vectors inside
-            let inner = ProjectionTy { trait_ref: trait_ref, item_name: item_name };
+            let inner = ProjectionTy::from_ref_and_name(self, trait_ref, item_name);
             self.mk_ty(TyProjection(inner))
         }
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index aeffd71a09649..22fcc61953b2b 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1051,8 +1051,8 @@ pub struct ProjectionPredicate<'tcx> {
 pub type PolyProjectionPredicate<'tcx> = Binder<ProjectionPredicate<'tcx>>;
 
 impl<'tcx> PolyProjectionPredicate<'tcx> {
-    pub fn item_name(&self) -> Name {
-        self.0.projection_ty.item_name // safe to skip the binder to access a name
+    pub fn item_name(&self, tcx: TyCtxt) -> Name {
+        self.0.projection_ty.item_name(tcx) // safe to skip the binder to access a name
     }
 }
 
diff --git a/src/librustc/ty/relate.rs b/src/librustc/ty/relate.rs
index bbe682e74bc04..d4f06a902eeaa 100644
--- a/src/librustc/ty/relate.rs
+++ b/src/librustc/ty/relate.rs
@@ -225,12 +225,13 @@ impl<'tcx> Relate<'tcx> for ty::ProjectionTy<'tcx> {
                            -> RelateResult<'tcx, ty::ProjectionTy<'tcx>>
         where R: TypeRelation<'a, 'gcx, 'tcx>, 'gcx: 'a+'tcx, 'tcx: 'a
     {
-        if a.item_name != b.item_name {
+        let tcx = relation.tcx();
+        if a.item_name(tcx) != b.item_name(tcx) {
             Err(TypeError::ProjectionNameMismatched(
-                expected_found(relation, &a.item_name, &b.item_name)))
+                expected_found(relation, &a.item_name(tcx), &b.item_name(tcx))))
         } else {
             let trait_ref = relation.relate(&a.trait_ref, &b.trait_ref)?;
-            Ok(ty::ProjectionTy { trait_ref: trait_ref, item_name: a.item_name })
+            Ok(ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, a.item_name(tcx)))
         }
     }
 }
@@ -457,7 +458,7 @@ pub fn super_relate_tys<'a, 'gcx, 'tcx, R>(relation: &mut R,
         (&ty::TyProjection(ref a_data), &ty::TyProjection(ref b_data)) =>
         {
             let projection_ty = relation.relate(a_data, b_data)?;
-            Ok(tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name))
+            Ok(tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name(tcx)))
         }
 
         (&ty::TyAnon(a_def_id, a_substs), &ty::TyAnon(b_def_id, b_substs))
diff --git a/src/librustc/ty/structural_impls.rs b/src/librustc/ty/structural_impls.rs
index 53d516e581b2a..c3ca679153759 100644
--- a/src/librustc/ty/structural_impls.rs
+++ b/src/librustc/ty/structural_impls.rs
@@ -135,10 +135,7 @@ impl<'a, 'tcx> Lift<'tcx> for ty::ProjectionTy<'a> {
     fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>)
                              -> Option<ty::ProjectionTy<'tcx>> {
         tcx.lift(&self.trait_ref).map(|trait_ref| {
-            ty::ProjectionTy {
-                trait_ref: trait_ref,
-                item_name: self.item_name
-            }
+            ty::ProjectionTy::from_ref_and_name(tcx, trait_ref, self.item_name(tcx))
         })
     }
 }
@@ -771,7 +768,7 @@ impl<'tcx> TypeFoldable<'tcx> for ty::ProjectionTy<'tcx> {
     fn super_fold_with<'gcx: 'tcx, F: TypeFolder<'gcx, 'tcx>>(&self, folder: &mut F) -> Self {
         ty::ProjectionTy {
             trait_ref: self.trait_ref.fold_with(folder),
-            item_name: self.item_name,
+            item_def_id: self.item_def_id,
         }
     }
 
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index 348d164af4190..bbb399434d6ae 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -556,9 +556,34 @@ pub struct ProjectionTy<'tcx> {
     /// The trait reference `T as Trait<..>`.
     pub trait_ref: ty::TraitRef<'tcx>,
 
-    /// The name `N` of the associated type.
-    pub item_name: Name,
+    /// The DefId of the TraitItem for the associated type N.
+    ///
+    /// Note that this is not the DefId of the TraitRef containing this
+    /// associated type, which is in tcx.associated_item(item_def_id).container.
+    pub item_def_id: DefId,
 }
+
+impl<'a, 'tcx> ProjectionTy<'tcx> {
+    /// Construct a ProjectionTy by searching the trait from trait_ref for the
+    /// associated item named item_name.
+    pub fn from_ref_and_name(
+        tcx: TyCtxt, trait_ref: ty::TraitRef<'tcx>, item_name: Name
+    ) -> ProjectionTy<'tcx> {
+        let item_def_id = tcx.associated_items(trait_ref.def_id).find(
+            |item| item.name == item_name).unwrap().def_id;
+
+        ProjectionTy {
+            trait_ref: trait_ref,
+            item_def_id: item_def_id,
+        }
+    }
+
+    pub fn item_name(self, tcx: TyCtxt) -> Name {
+        tcx.associated_item(self.item_def_id).name
+    }
+}
+
+
 /// Signature of a function type, which I have arbitrarily
 /// decided to use to refer to the input/output types.
 ///
@@ -871,10 +896,10 @@ impl<'a, 'tcx, 'gcx> ExistentialProjection<'tcx> {
         assert!(!self_ty.has_escaping_regions());
 
         ty::ProjectionPredicate {
-            projection_ty: ty::ProjectionTy {
-                trait_ref: self.trait_ref.with_self_ty(tcx, self_ty),
-                item_name: self.item_name,
-            },
+            projection_ty: ty::ProjectionTy::from_ref_and_name(
+                tcx,
+                self.trait_ref.with_self_ty(tcx, self_ty),
+                self.item_name),
             ty: self.ty,
         }
     }
diff --git a/src/librustc/ty/util.rs b/src/librustc/ty/util.rs
index 8edae027dbfbc..ce0f1ed5bb86c 100644
--- a/src/librustc/ty/util.rs
+++ b/src/librustc/ty/util.rs
@@ -691,8 +691,7 @@ impl<'a, 'gcx, 'tcx, W> TypeVisitor<'tcx> for TypeIdHasher<'a, 'gcx, 'tcx, W>
                 self.hash(p.name.as_str());
             }
             TyProjection(ref data) => {
-                self.def_id(data.trait_ref.def_id);
-                self.hash(data.item_name.as_str());
+                self.def_id(data.item_def_id);
             }
             TyNever |
             TyBool |
diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs
index 340e4f2cfccbc..5a1b7393db312 100644
--- a/src/librustc/util/ppaux.rs
+++ b/src/librustc/util/ppaux.rs
@@ -216,9 +216,11 @@ pub fn parameterized(f: &mut fmt::Formatter,
 
     for projection in projections {
         start_or_continue(f, "<", ", ")?;
-        write!(f, "{}={}",
-               projection.projection_ty.item_name,
-               projection.ty)?;
+        ty::tls::with(|tcx|
+            write!(f, "{}={}",
+            projection.projection_ty.item_name(tcx),
+            projection.ty)
+        )?;
     }
 
     start_or_continue(f, "", ">")?;
@@ -929,9 +931,10 @@ impl<'tcx> fmt::Display for ty::ProjectionPredicate<'tcx> {
 
 impl<'tcx> fmt::Display for ty::ProjectionTy<'tcx> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let item_name = ty::tls::with(|tcx| self.item_name(tcx));
         write!(f, "{:?}::{}",
                self.trait_ref,
-               self.item_name)
+               item_name)
     }
 }
 
diff --git a/src/librustc_save_analysis/lib.rs b/src/librustc_save_analysis/lib.rs
index d83740936d5d4..fa74e4d6ffccc 100644
--- a/src/librustc_save_analysis/lib.rs
+++ b/src/librustc_save_analysis/lib.rs
@@ -618,7 +618,7 @@ impl<'l, 'tcx: 'l> SaveContext<'l, 'tcx> {
                             if let ty::TyProjection(proj) = ty.sty {
                                 for item in self.tcx.associated_items(proj.trait_ref.def_id) {
                                     if item.kind == ty::AssociatedKind::Type {
-                                        if item.name == proj.item_name {
+                                        if item.name == proj.item_name(self.tcx) {
                                             return Def::AssociatedTy(item.def_id);
                                         }
                                     }
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index c9eb9807c41a5..212461a6d70e2 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -553,10 +553,11 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
         if self.trait_defines_associated_type_named(trait_ref.def_id(), binding.item_name) {
             return Ok(trait_ref.map_bound(|trait_ref| {
                 ty::ProjectionPredicate {
-                    projection_ty: ty::ProjectionTy {
-                        trait_ref: trait_ref,
-                        item_name: binding.item_name,
-                    },
+                    projection_ty: ty::ProjectionTy::from_ref_and_name(
+                        tcx,
+                        trait_ref,
+                        binding.item_name,
+                    ),
                     ty: binding.ty,
                 }
             }));
@@ -575,10 +576,11 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
 
         Ok(candidate.map_bound(|trait_ref| {
             ty::ProjectionPredicate {
-                projection_ty: ty::ProjectionTy {
-                    trait_ref: trait_ref,
-                    item_name: binding.item_name,
-                },
+                projection_ty: ty::ProjectionTy::from_ref_and_name(
+                    tcx,
+                    trait_ref,
+                    binding.item_name,
+                ),
                 ty: binding.ty,
             }
         }))
@@ -652,7 +654,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
                 let p = b.projection_ty;
                 ty::ExistentialProjection {
                     trait_ref: self.trait_ref_to_existential(p.trait_ref),
-                    item_name: p.item_name,
+                    item_name: p.item_name(tcx),
                     ty: b.ty
                 }
             })
@@ -679,7 +681,7 @@ impl<'o, 'gcx: 'tcx, 'tcx> AstConv<'gcx, 'tcx>+'o {
 
         for projection_bound in &projection_bounds {
             let pair = (projection_bound.0.projection_ty.trait_ref.def_id,
-                        projection_bound.0.projection_ty.item_name);
+                        projection_bound.0.projection_ty.item_name(tcx));
             associated_types.remove(&pair);
         }
 
diff --git a/src/librustc_typeck/check/autoderef.rs b/src/librustc_typeck/check/autoderef.rs
index f03451c04ed00..7d3a63263edbf 100644
--- a/src/librustc_typeck/check/autoderef.rs
+++ b/src/librustc_typeck/check/autoderef.rs
@@ -124,10 +124,11 @@ impl<'a, 'gcx, 'tcx> Autoderef<'a, 'gcx, 'tcx> {
         }
 
         let normalized = traits::normalize_projection_type(&mut selcx,
-                                                           ty::ProjectionTy {
-                                                               trait_ref: trait_ref,
-                                                               item_name: Symbol::intern("Target"),
-                                                           },
+                                                           ty::ProjectionTy::from_ref_and_name(
+                                                               tcx,
+                                                               trait_ref,
+                                                               Symbol::intern("Target"),
+                                                           ),
                                                            cause,
                                                            0);
 
diff --git a/src/librustc_typeck/check/regionck.rs b/src/librustc_typeck/check/regionck.rs
index b29bf01ba1996..fd26ff65661ca 100644
--- a/src/librustc_typeck/check/regionck.rs
+++ b/src/librustc_typeck/check/regionck.rs
@@ -1651,8 +1651,8 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
                declared_bounds, projection_ty);
 
         // see the extensive comment in projection_must_outlive
-
-        let ty = self.tcx.mk_projection(projection_ty.trait_ref, projection_ty.item_name);
+        let item_name = projection_ty.item_name(self.tcx);
+        let ty = self.tcx.mk_projection(projection_ty.trait_ref, item_name);
         let recursive_bound = self.recursive_type_bound(span, ty);
 
         VerifyBound::AnyRegion(declared_bounds).or(recursive_bound)
@@ -1718,9 +1718,9 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
     {
         debug!("projection_bounds(projection_ty={:?})",
                projection_ty);
-
+        let item_name = projection_ty.item_name(self.tcx);
         let ty = self.tcx.mk_projection(projection_ty.trait_ref.clone(),
-                                        projection_ty.item_name);
+                                        item_name);
 
         // Say we have a projection `<T as SomeTrait<'a>>::SomeType`. We are interested
         // in looking for a trait definition like:
@@ -1758,7 +1758,7 @@ impl<'a, 'gcx, 'tcx> RegionCtxt<'a, 'gcx, 'tcx> {
                     let (outlives, _) =
                         self.replace_late_bound_regions_with_fresh_var(
                             span,
-                            infer::AssocTypeProjection(projection_ty.item_name),
+                            infer::AssocTypeProjection(projection_ty.item_name(self.tcx)),
                             &outlives);
 
                     debug!("projection_bounds: outlives={:?} (3)",
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index 593477b066583..9464ac83870d9 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -955,7 +955,7 @@ impl<'tcx> Clean<Type> for ty::ProjectionTy<'tcx> {
             }
         };
         Type::QPath {
-            name: self.item_name.clean(cx),
+            name: self.item_name(cx.tcx).clean(cx),
             self_type: box self.trait_ref.self_ty().clean(cx),
             trait_: box trait_
         }