diff --git a/compiler/rustc_middle/src/mir/consts.rs b/compiler/rustc_middle/src/mir/consts.rs
index 164433aede263..5764a9c84eeaf 100644
--- a/compiler/rustc_middle/src/mir/consts.rs
+++ b/compiler/rustc_middle/src/mir/consts.rs
@@ -579,7 +579,7 @@ impl<'tcx> Display for Const<'tcx> {
 }
 
 ///////////////////////////////////////////////////////////////////////////
-/// Const-related utilities
+// Const-related utilities
 
 impl<'tcx> TyCtxt<'tcx> {
     pub fn span_as_caller_location(self, span: Span) -> ConstValue {
diff --git a/compiler/rustc_middle/src/mir/statement.rs b/compiler/rustc_middle/src/mir/statement.rs
index 6e52bc775ef73..ec2a8e86077d0 100644
--- a/compiler/rustc_middle/src/mir/statement.rs
+++ b/compiler/rustc_middle/src/mir/statement.rs
@@ -408,14 +408,14 @@ impl<'tcx> Place<'tcx> {
         self.as_ref().project_deeper(more_projections, tcx)
     }
 
-    pub fn ty_from<D: ?Sized>(
+    pub fn ty_from<D>(
         local: Local,
         projection: &[PlaceElem<'tcx>],
         local_decls: &D,
         tcx: TyCtxt<'tcx>,
     ) -> PlaceTy<'tcx>
     where
-        D: HasLocalDecls<'tcx>,
+        D: ?Sized + HasLocalDecls<'tcx>,
     {
         PlaceTy::from_ty(local_decls.local_decls()[local].ty).multi_projection_ty(tcx, projection)
     }
@@ -529,9 +529,9 @@ impl<'tcx> PlaceRef<'tcx> {
         Place { local: self.local, projection: tcx.mk_place_elems(new_projections) }
     }
 
-    pub fn ty<D: ?Sized>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> PlaceTy<'tcx>
+    pub fn ty<D>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> PlaceTy<'tcx>
     where
-        D: HasLocalDecls<'tcx>,
+        D: ?Sized + HasLocalDecls<'tcx>,
     {
         Place::ty_from(self.local, self.projection, local_decls, tcx)
     }
@@ -630,9 +630,9 @@ impl<'tcx> Operand<'tcx> {
         if let ty::FnDef(def_id, args) = *const_ty.kind() { Some((def_id, args)) } else { None }
     }
 
-    pub fn ty<D: ?Sized>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> Ty<'tcx>
+    pub fn ty<D>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> Ty<'tcx>
     where
-        D: HasLocalDecls<'tcx>,
+        D: ?Sized + HasLocalDecls<'tcx>,
     {
         match self {
             &Operand::Copy(ref l) | &Operand::Move(ref l) => l.ty(local_decls, tcx).ty,
@@ -640,9 +640,9 @@ impl<'tcx> Operand<'tcx> {
         }
     }
 
-    pub fn span<D: ?Sized>(&self, local_decls: &D) -> Span
+    pub fn span<D>(&self, local_decls: &D) -> Span
     where
-        D: HasLocalDecls<'tcx>,
+        D: ?Sized + HasLocalDecls<'tcx>,
     {
         match self {
             &Operand::Copy(ref l) | &Operand::Move(ref l) => {
@@ -674,7 +674,7 @@ impl<'tcx> ConstOperand<'tcx> {
 }
 
 ///////////////////////////////////////////////////////////////////////////
-/// Rvalues
+// Rvalues
 
 pub enum RvalueInitializationState {
     Shallow,
@@ -721,9 +721,9 @@ impl<'tcx> Rvalue<'tcx> {
         }
     }
 
-    pub fn ty<D: ?Sized>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> Ty<'tcx>
+    pub fn ty<D>(&self, local_decls: &D, tcx: TyCtxt<'tcx>) -> Ty<'tcx>
     where
-        D: HasLocalDecls<'tcx>,
+        D: ?Sized + HasLocalDecls<'tcx>,
     {
         match *self {
             Rvalue::Use(ref operand) => operand.ty(local_decls, tcx),
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 95759d1f31a7f..3f37595d0eef0 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -216,10 +216,7 @@ impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::ParamEnv<'tcx> {
 #[inline]
 fn decode_arena_allocable<'tcx, D: TyDecoder<'tcx>, T: ArenaAllocatable<'tcx> + Decodable<D>>(
     decoder: &mut D,
-) -> &'tcx T
-where
-    D: TyDecoder<'tcx>,
-{
+) -> &'tcx T {
     decoder.interner().arena.alloc(Decodable::decode(decoder))
 }
 
@@ -230,10 +227,7 @@ fn decode_arena_allocable_slice<
     T: ArenaAllocatable<'tcx> + Decodable<D>,
 >(
     decoder: &mut D,
-) -> &'tcx [T]
-where
-    D: TyDecoder<'tcx>,
-{
+) -> &'tcx [T] {
     decoder.interner().arena.alloc_from_iter(<Vec<T> as Decodable<D>>::decode(decoder))
 }