diff --git a/src/librustc/middle/traits/fulfill.rs b/src/librustc/middle/traits/fulfill.rs
index bf4273dbfd08..25c86be993f7 100644
--- a/src/librustc/middle/traits/fulfill.rs
+++ b/src/librustc/middle/traits/fulfill.rs
@@ -11,6 +11,8 @@
 use middle::mem_categorization::Typer;
 use middle::ty;
 use middle::typeck::infer::InferCtxt;
+use std::collections::HashSet;
+use std::rc::Rc;
 use util::ppaux::Repr;
 
 use super::CodeAmbiguity;
@@ -30,6 +32,13 @@ use super::select::SelectionContext;
 /// method `select_all_or_error` can be used to report any remaining
 /// ambiguous cases as errors.
 pub struct FulfillmentContext<'tcx> {
+    // a simple cache that aims to cache *exact duplicate obligations*
+    // and avoid adding them twice. This serves a different purpose
+    // than the `SelectionCache`: it avoids duplicate errors and
+    // permits recursive obligations, which are often generated from
+    // traits like `Send` et al.
+    duplicate_set: HashSet<Rc<ty::TraitRef<'tcx>>>,
+
     // A list of all obligations that have been registered with this
     // fulfillment context.
     trait_obligations: Vec<Obligation<'tcx>>,
@@ -43,6 +52,7 @@ pub struct FulfillmentContext<'tcx> {
 impl<'tcx> FulfillmentContext<'tcx> {
     pub fn new() -> FulfillmentContext<'tcx> {
         FulfillmentContext {
+            duplicate_set: HashSet::new(),
             trait_obligations: Vec::new(),
             attempted_mark: 0,
         }
@@ -52,9 +62,13 @@ impl<'tcx> FulfillmentContext<'tcx> {
                                tcx: &ty::ctxt<'tcx>,
                                obligation: Obligation<'tcx>)
     {
-        debug!("register_obligation({})", obligation.repr(tcx));
-        assert!(!obligation.trait_ref.has_escaping_regions());
-        self.trait_obligations.push(obligation);
+        if self.duplicate_set.insert(obligation.trait_ref.clone()) {
+            debug!("register_obligation({})", obligation.repr(tcx));
+            assert!(!obligation.trait_ref.has_escaping_regions());
+            self.trait_obligations.push(obligation);
+        } else {
+            debug!("register_obligation({}) -- already seen, skip", obligation.repr(tcx));
+        }
     }
 
     pub fn select_all_or_error<'a>(&mut self,
diff --git a/src/librustc/middle/traits/select.rs b/src/librustc/middle/traits/select.rs
index 9ce6947731dc..71a183b475c6 100644
--- a/src/librustc/middle/traits/select.rs
+++ b/src/librustc/middle/traits/select.rs
@@ -113,7 +113,7 @@ pub enum MethodMatchedData {
 /// candidate is one that might match or might not, depending on how
 /// type variables wind up being resolved. This only occurs during inference.
 ///
-/// For selection to suceed, there must be exactly one non-ambiguous
+/// For selection to succeed, there must be exactly one non-ambiguous
 /// candidate.  Usually, it is not possible to have more than one
 /// definitive candidate, due to the coherence rules. However, there is
 /// one case where it could occur: if there is a blanket impl for a
@@ -1149,24 +1149,12 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                              candidates: &mut CandidateSet<'tcx>)
                                              -> Result<(),SelectionError<'tcx>>
     {
-        // FIXME -- To be more like a normal impl, we should just
-        // ignore the nested cases here, and instead generate nested
-        // obligations in `confirm_candidate`. However, this doesn't
-        // work because we require handling the recursive cases to
-        // avoid infinite cycles (that is, with recursive types,
-        // sometimes `Foo : Copy` only holds if `Foo : Copy`).
-
         match self.builtin_bound(bound, stack.obligation.self_ty()) {
-            Ok(If(nested)) => {
-                debug!("builtin_bound: bound={} nested={}",
-                       bound.repr(self.tcx()),
-                       nested.repr(self.tcx()));
-                let data = self.vtable_builtin_data(stack.obligation, bound, nested);
-                match self.winnow_selection(Some(stack), VtableBuiltin(data)) {
-                    EvaluatedToOk => { Ok(candidates.vec.push(BuiltinCandidate(bound))) }
-                    EvaluatedToAmbig => { Ok(candidates.ambiguous = true) }
-                    EvaluatedToErr => { Err(Unimplemented) }
-                }
+            Ok(If(_)) => {
+                debug!("builtin_bound: bound={}",
+                       bound.repr(self.tcx()));
+                candidates.vec.push(BuiltinCandidate(bound));
+                Ok(())
             }
             Ok(ParameterBuiltin) => { Ok(()) }
             Ok(AmbiguousBuiltin) => { Ok(candidates.ambiguous = true) }
@@ -1539,8 +1527,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                candidate.repr(self.tcx()));
 
         match candidate {
-            // FIXME -- see assemble_builtin_bound_candidates()
-            BuiltinCandidate(_) |
+            BuiltinCandidate(builtin_bound) => {
+                Ok(VtableBuiltin(
+                    try!(self.confirm_builtin_candidate(obligation, builtin_bound))))
+            }
+
             ErrorCandidate => {
                 Ok(VtableBuiltin(VtableBuiltinData { nested: VecPerParamSpace::empty() }))
             }
@@ -1590,8 +1581,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         match try!(self.builtin_bound(bound, obligation.self_ty())) {
             If(nested) => Ok(self.vtable_builtin_data(obligation, bound, nested)),
-            AmbiguousBuiltin |
-            ParameterBuiltin => {
+            AmbiguousBuiltin | ParameterBuiltin => {
                 self.tcx().sess.span_bug(
                     obligation.cause.span,
                     format!("builtin bound for {} was ambig",