diff --git a/src/librustc/infer/canonical/mod.rs b/src/librustc/infer/canonical/mod.rs
index 274dbd1efd5d..9c616edba9f9 100644
--- a/src/librustc/infer/canonical/mod.rs
+++ b/src/librustc/infer/canonical/mod.rs
@@ -189,11 +189,16 @@ pub enum CanonicalTyVarKind {
 #[derive(Clone, Debug, HashStable)]
 pub struct QueryResponse<'tcx, R> {
     pub var_values: CanonicalVarValues<'tcx>,
-    pub region_constraints: Vec<QueryOutlivesConstraint<'tcx>>,
+    pub region_constraints: QueryRegionConstraints<'tcx>,
     pub certainty: Certainty,
     pub value: R,
 }
 
+#[derive(Clone, Debug, Default, HashStable)]
+pub struct QueryRegionConstraints<'tcx> {
+    outlives: Vec<QueryOutlivesConstraint<'tcx>>,
+}
+
 pub type Canonicalized<'tcx, V> = Canonical<'tcx, V>;
 
 pub type CanonicalizedQueryResponse<'tcx, T> =
@@ -540,6 +545,19 @@ BraceStructLiftImpl! {
     } where R: Lift<'tcx>
 }
 
+BraceStructTypeFoldableImpl! {
+    impl<'tcx> TypeFoldable<'tcx> for QueryRegionConstraints<'tcx> {
+        outlives
+    }
+}
+
+BraceStructLiftImpl! {
+    impl<'a, 'tcx> Lift<'tcx> for QueryRegionConstraints<'a> {
+        type Lifted = QueryRegionConstraints<'tcx>;
+        outlives
+    }
+}
+
 impl<'tcx> Index<BoundVar> for CanonicalVarValues<'tcx> {
     type Output = Kind<'tcx>;
 
diff --git a/src/librustc/infer/canonical/query_response.rs b/src/librustc/infer/canonical/query_response.rs
index c72af20a8630..acaed1893977 100644
--- a/src/librustc/infer/canonical/query_response.rs
+++ b/src/librustc/infer/canonical/query_response.rs
@@ -11,7 +11,7 @@ use crate::arena::ArenaAllocatable;
 use crate::infer::canonical::substitute::substitute_value;
 use crate::infer::canonical::{
     Canonical, CanonicalVarValues, CanonicalizedQueryResponse, Certainty,
-    OriginalQueryValues, QueryOutlivesConstraint, QueryResponse,
+    OriginalQueryValues, QueryRegionConstraints, QueryOutlivesConstraint, QueryResponse,
 };
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::InferCtxtBuilder;
@@ -132,7 +132,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
     {
         self.canonicalize_response(&QueryResponse {
             var_values: inference_vars,
-            region_constraints: vec![],
+            region_constraints: QueryRegionConstraints::default(),
             certainty: Certainty::Proven, // Ambiguities are OK!
             value: answer,
         })
@@ -173,7 +173,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         debug!("ambig_errors = {:#?}", ambig_errors);
 
         let region_obligations = self.take_registered_region_obligations();
-        let region_constraints = self.with_region_constraints(|region_constraints| {
+        let outlives_constraints = self.with_region_constraints(|region_constraints| {
             make_query_outlives(
                 tcx,
                 region_obligations
@@ -191,7 +191,9 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
         Ok(QueryResponse {
             var_values: inference_vars,
-            region_constraints,
+            region_constraints: QueryRegionConstraints {
+                outlives: outlives_constraints,
+            },
             certainty,
             value: answer,
         })
@@ -225,7 +227,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         obligations.extend(self.query_outlives_constraints_into_obligations(
             cause,
             param_env,
-            &query_response.value.region_constraints,
+            &query_response.value.region_constraints.outlives,
             &result_subst,
         ));
 
@@ -334,7 +336,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
 
         // ...also include the other query region constraints from the query.
         output_query_outlives_constraints.extend(
-            query_response.value.region_constraints.iter().filter_map(|r_c| {
+            query_response.value.region_constraints.outlives.iter().filter_map(|r_c| {
                 let r_c = substitute_value(self.tcx, &result_subst, r_c);
 
                 // Screen out `'a: 'a` cases -- we skip the binder here but
diff --git a/src/librustc_traits/chalk_context/mod.rs b/src/librustc_traits/chalk_context/mod.rs
index bbb0825ee082..5c23ad4a4edf 100644
--- a/src/librustc_traits/chalk_context/mod.rs
+++ b/src/librustc_traits/chalk_context/mod.rs
@@ -17,6 +17,7 @@ use rustc::infer::canonical::{
     CanonicalVarValues,
     OriginalQueryValues,
     QueryResponse,
+    QueryRegionConstraints,
     Certainty,
 };
 use rustc::traits::{
@@ -151,14 +152,14 @@ impl context::AggregateOps<ChalkArenas<'tcx>> for ChalkContext<'tcx> {
         let solution = constrained_subst.unchecked_map(|cs| match ambiguous {
             true => QueryResponse {
                 var_values: cs.subst.make_identity(self.tcx),
-                region_constraints: Vec::new(),
+                region_constraints: QueryRegionConstraints::default(),
                 certainty: Certainty::Ambiguous,
                 value: (),
             },
 
             false => QueryResponse {
                 var_values: cs.subst,
-                region_constraints: Vec::new(),
+                region_constraints: QueryRegionConstraints::default(),
 
                 // FIXME: restore this later once we get better at handling regions
                 // region_constraints: cs.constraints