diff --git a/src/librustc/ich/impls_mir.rs b/src/librustc/ich/impls_mir.rs
index 38a298d81dda..b660187945cd 100644
--- a/src/librustc/ich/impls_mir.rs
+++ b/src/librustc/ich/impls_mir.rs
@@ -597,6 +597,14 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for mir::UserTypeAnnotation<
             mir::UserTypeAnnotation::Ty(ref ty) => {
                 ty.hash_stable(hcx, hasher);
             }
+            mir::UserTypeAnnotation::FnDef(ref def_id, ref substs) => {
+                def_id.hash_stable(hcx, hasher);
+                substs.hash_stable(hcx, hasher);
+            }
+            mir::UserTypeAnnotation::AdtDef(ref def_id, ref substs) => {
+                def_id.hash_stable(hcx, hasher);
+                substs.hash_stable(hcx, hasher);
+            }
         }
     }
 }
diff --git a/src/librustc/mir/mod.rs b/src/librustc/mir/mod.rs
index eb4aa7ece49a..278a9bba1780 100644
--- a/src/librustc/mir/mod.rs
+++ b/src/librustc/mir/mod.rs
@@ -37,7 +37,7 @@ use syntax::ast::{self, Name};
 use syntax::symbol::InternedString;
 use syntax_pos::{Span, DUMMY_SP};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
-use ty::subst::{Subst, Substs};
+use ty::subst::{CanonicalSubsts, Subst, Substs};
 use ty::{self, AdtDef, CanonicalTy, ClosureSubsts, GeneratorSubsts, Region, Ty, TyCtxt};
 use util::ppaux;
 
@@ -2413,11 +2413,15 @@ pub struct Constant<'tcx> {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable)]
 pub enum UserTypeAnnotation<'tcx> {
     Ty(CanonicalTy<'tcx>),
+    FnDef(DefId, CanonicalSubsts<'tcx>),
+    AdtDef(&'tcx AdtDef, CanonicalSubsts<'tcx>),
 }
 
 EnumTypeFoldableImpl! {
     impl<'tcx> TypeFoldable<'tcx> for UserTypeAnnotation<'tcx> {
         (UserTypeAnnotation::Ty)(ty),
+        (UserTypeAnnotation::FnDef)(def, substs),
+        (UserTypeAnnotation::AdtDef)(def, substs),
     }
 }
 
diff --git a/src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs b/src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs
index 35d0b96b88a9..21dabd0c1bdb 100644
--- a/src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs
+++ b/src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs
@@ -71,9 +71,21 @@ pub(super) fn relate_type_and_user_type<'tcx>(
         a, v, user_ty, locations
     );
 
-    let (b, _values) = match user_ty {
+    let b = match user_ty {
         UserTypeAnnotation::Ty(canonical_ty) => {
-            infcx.instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_ty)
+            let (ty, _) =
+                infcx.instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_ty);
+            ty
+        }
+        UserTypeAnnotation::FnDef(def_id, canonical_substs) => {
+            let (substs, _) =
+                infcx.instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_substs);
+            infcx.tcx.mk_fn_def(def_id, substs)
+        }
+        UserTypeAnnotation::AdtDef(adt_def, canonical_substs) => {
+            let (substs, _) =
+                infcx.instantiate_canonical_with_fresh_inference_vars(DUMMY_SP, &canonical_substs);
+            infcx.tcx.mk_adt(adt_def, substs)
         }
     };
 
diff --git a/src/librustc_mir/hair/cx/expr.rs b/src/librustc_mir/hair/cx/expr.rs
index 4dc43a533cfc..984abb039265 100644
--- a/src/librustc_mir/hair/cx/expr.rs
+++ b/src/librustc_mir/hair/cx/expr.rs
@@ -295,13 +295,7 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                     let substs = cx.tables().node_substs(fun.hir_id);
 
                     let user_ty = cx.tables().user_substs(fun.hir_id)
-                        .map(|user_substs| {
-                            UserTypeAnnotation::Ty(user_substs.unchecked_map(|user_substs| {
-                                // Here, we just pair an `AdtDef` with the
-                                // `user_substs`, so no new types etc are introduced.
-                                cx.tcx().mk_adt(adt_def, user_substs)
-                            }))
-                        });
+                        .map(|user_substs| UserTypeAnnotation::AdtDef(adt_def, user_substs));
 
                     let field_refs = args.iter()
                         .enumerate()
@@ -774,14 +768,7 @@ fn user_substs_applied_to_def(
         Def::Method(_) |
         Def::StructCtor(_, CtorKind::Fn) |
         Def::VariantCtor(_, CtorKind::Fn) =>
-            Some(
-                UserTypeAnnotation::Ty(cx.tables().user_substs(hir_id)?.unchecked_map(|user_substs| {
-                        // Here, we just pair a `DefId` with the
-                        // `user_substs`, so no new types etc are introduced.
-                        cx.tcx().mk_fn_def(def.def_id(), user_substs)
-                    }),
-                )
-            ),
+            Some(UserTypeAnnotation::FnDef(def.def_id(), cx.tables().user_substs(hir_id)?)),
 
         Def::Const(_def_id) |
         Def::AssociatedConst(_def_id) =>
diff --git a/src/librustc_mir/hair/util.rs b/src/librustc_mir/hair/util.rs
index 46a957f453cb..71cbac6b7c88 100644
--- a/src/librustc_mir/hair/util.rs
+++ b/src/librustc_mir/hair/util.rs
@@ -23,13 +23,7 @@ crate trait UserAnnotatedTyHelpers<'gcx: 'tcx, 'tcx> {
         adt_def: &'tcx AdtDef,
     ) -> Option<UserTypeAnnotation<'tcx>> {
         let user_substs = self.tables().user_substs(hir_id)?;
-        Some(UserTypeAnnotation::Ty(user_substs.unchecked_map(
-            |user_substs| {
-                // Here, we just pair an `AdtDef` with the
-                // `user_substs`, so no new types etc are introduced.
-                self.tcx().mk_adt(adt_def, user_substs)
-            },
-        )))
+        Some(UserTypeAnnotation::AdtDef(adt_def, user_substs))
     }
 
     /// Looks up the type associated with this hir-id and applies the
@@ -41,21 +35,8 @@ crate trait UserAnnotatedTyHelpers<'gcx: 'tcx, 'tcx> {
     ) -> Option<UserTypeAnnotation<'tcx>> {
         let user_substs = self.tables().user_substs(hir_id)?;
         match &self.tables().node_id_to_type(hir_id).sty {
-            ty::Adt(adt_def, _) => Some(UserTypeAnnotation::Ty(user_substs.unchecked_map(
-                |user_substs| {
-                    // Ok to call `unchecked_map` because we just pair an
-                    // `AdtDef` with the `user_substs`, so no new types
-                    // etc are introduced.
-                    self.tcx().mk_adt(adt_def, user_substs)
-                },
-            ))),
-            ty::FnDef(def_id, _) => Some(UserTypeAnnotation::Ty(user_substs.unchecked_map(
-                |user_substs| {
-                    // Here, we just pair a `DefId` with the
-                    // `user_substs`, so no new types etc are introduced.
-                    self.tcx().mk_fn_def(*def_id, user_substs)
-                },
-            ))),
+            ty::Adt(adt_def, _) => Some(UserTypeAnnotation::AdtDef(adt_def, user_substs)),
+            ty::FnDef(def_id, _) => Some(UserTypeAnnotation::FnDef(*def_id, user_substs)),
             sty => bug!(
                 "sty: {:?} should not have user-substs {:?} recorded ",
                 sty,