diff --git a/src/librustc/infer/region_inference/graphviz.rs b/src/librustc/infer/region_inference/graphviz.rs
index 49f57d9aef50..efe364166e4b 100644
--- a/src/librustc/infer/region_inference/graphviz.rs
+++ b/src/librustc/infer/region_inference/graphviz.rs
@@ -30,6 +30,7 @@ use util::nodemap::{FxHashMap, FxHashSet};
 
 use std::borrow::Cow;
 use std::collections::hash_map::Entry::Vacant;
+use std::collections::btree_map::BTreeMap;
 use std::env;
 use std::fs::File;
 use std::io;
@@ -124,7 +125,7 @@ pub fn maybe_print_constraints_for<'a, 'gcx, 'tcx>(
 struct ConstraintGraph<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     graph_name: String,
     region_rels: &'a RegionRelations<'a, 'gcx, 'tcx>,
-    map: &'a FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
+    map: &'a BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
     node_ids: FxHashMap<Node, usize>,
 }
 
@@ -264,7 +265,7 @@ impl<'a, 'gcx, 'tcx> dot::GraphWalk<'a> for ConstraintGraph<'a, 'gcx, 'tcx> {
     }
 }
 
-pub type ConstraintMap<'tcx> = FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
+pub type ConstraintMap<'tcx> = BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;
 
 fn dump_region_constraints_to<'a, 'gcx, 'tcx>(region_rels: &RegionRelations<'a, 'gcx, 'tcx>,
                                               map: &ConstraintMap<'tcx>,
diff --git a/src/librustc/infer/region_inference/mod.rs b/src/librustc/infer/region_inference/mod.rs
index 4c8a72512f1d..f9f611c3970b 100644
--- a/src/librustc/infer/region_inference/mod.rs
+++ b/src/librustc/infer/region_inference/mod.rs
@@ -28,6 +28,7 @@ use ty::{Region, RegionVid};
 use ty::{ReEmpty, ReStatic, ReFree, ReEarlyBound, ReErased};
 use ty::{ReLateBound, ReScope, ReVar, ReSkolemized, BrFresh};
 
+use std::collections::BTreeMap;
 use std::cell::{Cell, RefCell};
 use std::fmt;
 use std::mem;
@@ -36,7 +37,7 @@ use std::u32;
 mod graphviz;
 
 /// A constraint that influences the inference process.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 pub enum Constraint<'tcx> {
     /// One region variable is subregion of another
     ConstrainVarSubVar(RegionVid, RegionVid),
@@ -186,7 +187,7 @@ pub struct RegionVarBindings<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     /// Constraints of the form `A <= B` introduced by the region
     /// checker.  Here at least one of `A` and `B` must be a region
     /// variable.
-    constraints: RefCell<FxHashMap<Constraint<'tcx>, SubregionOrigin<'tcx>>>,
+    constraints: RefCell<BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>>,
 
     /// A "verify" is something that we need to verify after inference is
     /// done, but which does not directly affect inference in any way.
@@ -357,7 +358,7 @@ impl<'a, 'gcx, 'tcx> RegionVarBindings<'a, 'gcx, 'tcx> {
             tcx,
             var_origins: RefCell::new(Vec::new()),
             values: RefCell::new(None),
-            constraints: RefCell::new(FxHashMap()),
+            constraints: RefCell::new(BTreeMap::new()),
             verifys: RefCell::new(Vec::new()),
             givens: RefCell::new(FxHashSet()),
             lubs: RefCell::new(FxHashMap()),
diff --git a/src/librustc/ty/sty.rs b/src/librustc/ty/sty.rs
index d0ac7d0183a5..a60cad0de9f7 100644
--- a/src/librustc/ty/sty.rs
+++ b/src/librustc/ty/sty.rs
@@ -760,7 +760,7 @@ impl<'a, 'gcx, 'tcx> ParamTy {
 /// is the outer fn.
 ///
 /// [dbi]: http://en.wikipedia.org/wiki/De_Bruijn_index
-#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, Copy)]
+#[derive(Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, Copy, PartialOrd, Ord)]
 pub struct DebruijnIndex {
     /// We maintain the invariant that this is never 0. So 1 indicates
     /// the innermost binder. To ensure this, create with `DebruijnIndex::new`.
@@ -825,7 +825,7 @@ pub type Region<'tcx> = &'tcx RegionKind;
 ///
 /// [1] http://smallcultfollowing.com/babysteps/blog/2013/10/29/intermingled-parameter-lists/
 /// [2] http://smallcultfollowing.com/babysteps/blog/2013/11/04/intermingled-parameter-lists/
-#[derive(Clone, PartialEq, Eq, Hash, Copy, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, Eq, Hash, Copy, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
 pub enum RegionKind {
     // Region bound in a type or fn declaration which will be
     // substituted 'early' -- that is, at the same time when type
@@ -871,7 +871,7 @@ pub enum RegionKind {
 
 impl<'tcx> serialize::UseSpecializedDecodable for Region<'tcx> {}
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, PartialOrd, Ord)]
 pub struct EarlyBoundRegion {
     pub def_id: DefId,
     pub index: u32,
@@ -893,12 +893,12 @@ pub struct FloatVid {
     pub index: u32,
 }
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy)]
+#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Copy, PartialOrd, Ord)]
 pub struct RegionVid {
     pub index: u32,
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
 pub struct SkolemizedRegionVid {
     pub index: u32,
 }
diff --git a/src/test/compile-fail/associated-types/cache/project-fn-ret-invariant.rs b/src/test/compile-fail/associated-types/cache/project-fn-ret-invariant.rs
index 0574d87e8715..59688362197c 100644
--- a/src/test/compile-fail/associated-types/cache/project-fn-ret-invariant.rs
+++ b/src/test/compile-fail/associated-types/cache/project-fn-ret-invariant.rs
@@ -60,8 +60,8 @@ fn baz<'a,'b>(x: Type<'a>) -> Type<'static> {
 
 #[cfg(krisskross)] // two instantiations, mixing and matching: BAD
 fn transmute<'a,'b>(x: Type<'a>, y: Type<'b>) -> (Type<'a>, Type<'b>) {
-   let a = bar(foo, y);
-   let b = bar(foo, x); //[krisskross]~ ERROR E0623
+   let a = bar(foo, y); //[krisskross]~ ERROR E0623
+   let b = bar(foo, x);
    (a, b) //[krisskross]~ ERROR E0623
 }