diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index cdc27244dde..122171e4691 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -28,6 +28,7 @@
 #![feature(rustc_diagnostic_macros)]
 #![feature(unboxed_closures)]
 #![feature(old_orphan_check)]
+#![feature(associated_types)]
 
 extern crate arena;
 extern crate flate;
diff --git a/src/librustc/metadata/encoder.rs b/src/librustc/metadata/encoder.rs
index 10383b901f3..17663a127a8 100644
--- a/src/librustc/metadata/encoder.rs
+++ b/src/librustc/metadata/encoder.rs
@@ -364,7 +364,7 @@ fn encode_enum_variant_info(ecx: &EncodeContext,
     }
 }
 
-fn encode_path<PI: Iterator<PathElem>>(rbml_w: &mut Encoder, path: PI) {
+fn encode_path<PI: Iterator<Item=PathElem>>(rbml_w: &mut Encoder, path: PI) {
     let path = path.collect::<Vec<_>>();
     rbml_w.start_tag(tag_path);
     rbml_w.wr_tagged_u32(tag_path_len, path.len() as u32);
diff --git a/src/librustc/middle/cfg/construct.rs b/src/librustc/middle/cfg/construct.rs
index 92aa70548c8..a7b28a6323e 100644
--- a/src/librustc/middle/cfg/construct.rs
+++ b/src/librustc/middle/cfg/construct.rs
@@ -150,7 +150,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         }
     }
 
-    fn pats_all<'b, I: Iterator<&'b P<ast::Pat>>>(&mut self,
+    fn pats_all<'b, I: Iterator<Item=&'b P<ast::Pat>>>(&mut self,
                                           pats: I,
                                           pred: CFGIndex) -> CFGIndex {
         //! Handles case where all of the patterns must match.
@@ -501,7 +501,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         }
     }
 
-    fn call<'b, I: Iterator<&'b ast::Expr>>(&mut self,
+    fn call<'b, I: Iterator<Item=&'b ast::Expr>>(&mut self,
             call_expr: &ast::Expr,
             pred: CFGIndex,
             func_or_rcvr: &ast::Expr,
@@ -521,7 +521,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         }
     }
 
-    fn exprs<'b, I: Iterator<&'b ast::Expr>>(&mut self,
+    fn exprs<'b, I: Iterator<Item=&'b ast::Expr>>(&mut self,
                                              exprs: I,
                                              pred: CFGIndex) -> CFGIndex {
         //! Constructs graph for `exprs` evaluated in order
@@ -535,7 +535,7 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> {
         opt_expr.iter().fold(pred, |p, e| self.expr(&**e, p))
     }
 
-    fn straightline<'b, I: Iterator<&'b ast::Expr>>(&mut self,
+    fn straightline<'b, I: Iterator<Item=&'b ast::Expr>>(&mut self,
                     expr: &ast::Expr,
                     pred: CFGIndex,
                     subexprs: I) -> CFGIndex {
diff --git a/src/librustc/middle/check_match.rs b/src/librustc/middle/check_match.rs
index d16224ec5b8..4151f5fa627 100644
--- a/src/librustc/middle/check_match.rs
+++ b/src/librustc/middle/check_match.rs
@@ -92,7 +92,7 @@ impl<'a> fmt::Show for Matrix<'a> {
 }
 
 impl<'a> FromIterator<Vec<&'a Pat>> for Matrix<'a> {
-    fn from_iter<T: Iterator<Vec<&'a Pat>>>(iterator: T) -> Matrix<'a> {
+    fn from_iter<T: Iterator<Item=Vec<&'a Pat>>>(iterator: T) -> Matrix<'a> {
         Matrix(iterator.collect())
     }
 }
diff --git a/src/librustc/middle/const_eval.rs b/src/librustc/middle/const_eval.rs
index 9fc5cb03353..96b2a62326b 100644
--- a/src/librustc/middle/const_eval.rs
+++ b/src/librustc/middle/const_eval.rs
@@ -81,7 +81,7 @@ pub fn join(a: constness, b: constness) -> constness {
     }
 }
 
-pub fn join_all<It: Iterator<constness>>(cs: It) -> constness {
+pub fn join_all<It: Iterator<Item=constness>>(cs: It) -> constness {
     cs.fold(integral_const, |a, b| join(a, b))
 }
 
diff --git a/src/librustc/middle/graph.rs b/src/librustc/middle/graph.rs
index da00d737b47..e8efdda3888 100644
--- a/src/librustc/middle/graph.rs
+++ b/src/librustc/middle/graph.rs
@@ -305,7 +305,9 @@ pub struct DepthFirstTraversal<'g, N:'g, E:'g> {
     visited: BitvSet
 }
 
-impl<'g, N, E> Iterator<&'g N> for DepthFirstTraversal<'g, N, E> {
+impl<'g, N, E> Iterator for DepthFirstTraversal<'g, N, E> {
+    type Item = &'g N;
+
     fn next(&mut self) -> Option<&'g N> {
         while let Some(idx) = self.stack.pop() {
             if !self.visited.insert(idx.node_id()) {
diff --git a/src/librustc/middle/subst.rs b/src/librustc/middle/subst.rs
index 97e74b9f6bb..e7971a82119 100644
--- a/src/librustc/middle/subst.rs
+++ b/src/librustc/middle/subst.rs
@@ -494,7 +494,9 @@ impl<'a,T> EnumeratedItems<'a,T> {
     }
 }
 
-impl<'a,T> Iterator<(ParamSpace, uint, &'a T)> for EnumeratedItems<'a,T> {
+impl<'a,T> Iterator for EnumeratedItems<'a,T> {
+    type Item = (ParamSpace, uint, &'a T);
+
     fn next(&mut self) -> Option<(ParamSpace, uint, &'a T)> {
         let spaces = ParamSpace::all();
         if self.space_index < spaces.len() {
diff --git a/src/librustc/middle/traits/select.rs b/src/librustc/middle/traits/select.rs
index d09f2a250b0..bd901ff431a 100644
--- a/src/librustc/middle/traits/select.rs
+++ b/src/librustc/middle/traits/select.rs
@@ -297,7 +297,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                                 stack: Option<&TraitObligationStack<'o, 'tcx>>,
                                                 mut predicates: I)
                                                 -> EvaluationResult<'tcx>
-        where I : Iterator<&'a PredicateObligation<'tcx>>, 'tcx:'a
+        where I : Iterator<Item=&'a PredicateObligation<'tcx>>, 'tcx:'a
     {
         let mut result = EvaluatedToOk;
         for obligation in predicates {
@@ -2315,9 +2315,9 @@ impl<'o, 'tcx> TraitObligationStack<'o, 'tcx> {
     }
 }
 
-impl<'o, 'tcx> Iterator<&'o TraitObligationStack<'o,'tcx>>
-           for Option<&'o TraitObligationStack<'o, 'tcx>>
-{
+impl<'o, 'tcx> Iterator for Option<&'o TraitObligationStack<'o, 'tcx>> {
+    type Item = &'o TraitObligationStack<'o,'tcx>;
+
     fn next(&mut self) -> Option<&'o TraitObligationStack<'o, 'tcx>> {
         match *self {
             Some(o) => {
diff --git a/src/librustc/middle/traits/util.rs b/src/librustc/middle/traits/util.rs
index 41a59d6a5d8..e4578f74763 100644
--- a/src/librustc/middle/traits/util.rs
+++ b/src/librustc/middle/traits/util.rs
@@ -133,7 +133,9 @@ impl<'cx, 'tcx> Elaborator<'cx, 'tcx> {
     }
 }
 
-impl<'cx, 'tcx> Iterator<ty::Predicate<'tcx>> for Elaborator<'cx, 'tcx> {
+impl<'cx, 'tcx> Iterator for Elaborator<'cx, 'tcx> {
+    type Item = ty::Predicate<'tcx>;
+
     fn next(&mut self) -> Option<ty::Predicate<'tcx>> {
         loop {
             // Extract next item from top-most stack frame, if any.
@@ -197,7 +199,9 @@ pub fn transitive_bounds<'cx, 'tcx>(tcx: &'cx ty::ctxt<'tcx>,
     elaborate_trait_refs(tcx, bounds).filter_to_traits()
 }
 
-impl<'cx, 'tcx> Iterator<ty::PolyTraitRef<'tcx>> for Supertraits<'cx, 'tcx> {
+impl<'cx, 'tcx> Iterator for Supertraits<'cx, 'tcx> {
+    type Item = ty::PolyTraitRef<'tcx>;
+
     fn next(&mut self) -> Option<ty::PolyTraitRef<'tcx>> {
         loop {
             match self.elaborator.next() {
diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index 999bc23c270..f786ef8afee 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -3716,10 +3716,10 @@ pub fn is_type_representable<'tcx>(cx: &ctxt<'tcx>, sp: Span, ty: Ty<'tcx>)
                                    -> Representability {
 
     // Iterate until something non-representable is found
-    fn find_nonrepresentable<'tcx, It: Iterator<Ty<'tcx>>>(cx: &ctxt<'tcx>, sp: Span,
-                                                           seen: &mut Vec<Ty<'tcx>>,
-                                                           iter: It)
-                                                           -> Representability {
+    fn find_nonrepresentable<'tcx, It: Iterator<Item=Ty<'tcx>>>(cx: &ctxt<'tcx>, sp: Span,
+                                                                seen: &mut Vec<Ty<'tcx>>,
+                                                                iter: It)
+                                                                -> Representability {
         iter.fold(Representable,
                   |r, ty| cmp::max(r, is_type_structurally_recursive(cx, sp, seen, ty)))
     }
diff --git a/src/librustc/middle/ty_walk.rs b/src/librustc/middle/ty_walk.rs
index 406ebf4bc38..12df36c10fc 100644
--- a/src/librustc/middle/ty_walk.rs
+++ b/src/librustc/middle/ty_walk.rs
@@ -94,7 +94,9 @@ impl<'tcx> TypeWalker<'tcx> {
     }
 }
 
-impl<'tcx> Iterator<Ty<'tcx>> for TypeWalker<'tcx> {
+impl<'tcx> Iterator for TypeWalker<'tcx> {
+    type Item = Ty<'tcx>;
+
     fn next(&mut self) -> Option<Ty<'tcx>> {
         debug!("next(): stack={}", self.stack);
         match self.stack.pop() {
diff --git a/src/librustc/session/search_paths.rs b/src/librustc/session/search_paths.rs
index 56b4cae2e43..14ea2d3d33a 100644
--- a/src/librustc/session/search_paths.rs
+++ b/src/librustc/session/search_paths.rs
@@ -53,7 +53,9 @@ impl SearchPaths {
     }
 }
 
-impl<'a> Iterator<&'a Path> for Iter<'a> {
+impl<'a> Iterator for Iter<'a> {
+    type Item = &'a Path;
+
     fn next(&mut self) -> Option<&'a Path> {
         loop {
             match self.iter.next() {