diff --git a/compiler/rustc_borrowck/src/type_check/mod.rs b/compiler/rustc_borrowck/src/type_check/mod.rs
index 7d19b57e40c5..d661fb6403c9 100644
--- a/compiler/rustc_borrowck/src/type_check/mod.rs
+++ b/compiler/rustc_borrowck/src/type_check/mod.rs
@@ -1456,78 +1456,79 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                     }
                     CastKind::PtrToPtr => {
                         let ty_from = op.ty(self.body, tcx);
-                        let cast_ty_from = CastTy::from_ty(ty_from);
-                        let cast_ty_to = CastTy::from_ty(*ty);
+                        let Some(CastTy::Ptr(src)) = CastTy::from_ty(ty_from) else {
+                            unreachable!();
+                        };
+                        let Some(CastTy::Ptr(dst)) = CastTy::from_ty(*ty) else {
+                            unreachable!();
+                        };
 
-                        match (cast_ty_from, cast_ty_to) {
-                            (Some(CastTy::Ptr(src)), Some(CastTy::Ptr(dst))) => {
-                                if self
-                                    .infcx
-                                    .type_is_sized_modulo_regions(self.infcx.param_env, dst.ty)
-                                {
-                                    // Wide to thin ptr cast. This may even occur in an env with
-                                    // impossible predicates, such as `where dyn Trait: Sized`.
-                                    // In this case, we don't want to fall into the case below,
-                                    // since the types may not actually be equatable, but it's
-                                    // fine to perform this operation in an impossible env.
-                                } else if let ty::Dynamic(src_tty, _src_lt, ty::Dyn) =
-                                    *self.struct_tail(src.ty, location).kind()
-                                    && let ty::Dynamic(dst_tty, dst_lt, ty::Dyn) =
-                                        *self.struct_tail(dst.ty, location).kind()
-                                    && src_tty.principal().is_some()
-                                    && dst_tty.principal().is_some()
-                                {
-                                    // This checks (lifetime part of) vtable validity for pointer casts,
-                                    // which is irrelevant when there are aren't principal traits on
-                                    // both sides (aka only auto traits).
-                                    //
-                                    // Note that other checks (such as denying `dyn Send` -> `dyn
-                                    // Debug`) are in `rustc_hir_typeck`.
+                        if self.infcx.type_is_sized_modulo_regions(self.infcx.param_env, dst.ty) {
+                            // Wide to thin ptr cast. This may even occur in an env with
+                            // impossible predicates, such as `where dyn Trait: Sized`.
+                            // In this case, we don't want to fall into the case below,
+                            // since the types may not actually be equatable, but it's
+                            // fine to perform this operation in an impossible env.
+                            let trait_ref = ty::TraitRef::new(
+                                tcx,
+                                tcx.require_lang_item(LangItem::Sized, self.last_span),
+                                [dst.ty],
+                            );
+                            self.prove_trait_ref(
+                                trait_ref,
+                                location.to_locations(),
+                                ConstraintCategory::Cast {
+                                    is_implicit_coercion: true,
+                                    unsize_to: None,
+                                },
+                            );
+                        } else if let ty::Dynamic(src_tty, _src_lt, ty::Dyn) =
+                            *self.struct_tail(src.ty, location).kind()
+                            && let ty::Dynamic(dst_tty, dst_lt, ty::Dyn) =
+                                *self.struct_tail(dst.ty, location).kind()
+                            && src_tty.principal().is_some()
+                            && dst_tty.principal().is_some()
+                        {
+                            // This checks (lifetime part of) vtable validity for pointer casts,
+                            // which is irrelevant when there are aren't principal traits on
+                            // both sides (aka only auto traits).
+                            //
+                            // Note that other checks (such as denying `dyn Send` -> `dyn
+                            // Debug`) are in `rustc_hir_typeck`.
 
-                                    // Remove auto traits.
-                                    // Auto trait checks are handled in `rustc_hir_typeck` as FCW.
-                                    let src_obj = Ty::new_dynamic(
-                                        tcx,
-                                        tcx.mk_poly_existential_predicates(
-                                            &src_tty.without_auto_traits().collect::<Vec<_>>(),
-                                        ),
-                                        // FIXME: Once we disallow casting `*const dyn Trait + 'short`
-                                        // to `*const dyn Trait + 'long`, then this can just be `src_lt`.
-                                        dst_lt,
-                                        ty::Dyn,
-                                    );
-                                    let dst_obj = Ty::new_dynamic(
-                                        tcx,
-                                        tcx.mk_poly_existential_predicates(
-                                            &dst_tty.without_auto_traits().collect::<Vec<_>>(),
-                                        ),
-                                        dst_lt,
-                                        ty::Dyn,
-                                    );
+                            // Remove auto traits.
+                            // Auto trait checks are handled in `rustc_hir_typeck` as FCW.
+                            let src_obj = Ty::new_dynamic(
+                                tcx,
+                                tcx.mk_poly_existential_predicates(
+                                    &src_tty.without_auto_traits().collect::<Vec<_>>(),
+                                ),
+                                // FIXME: Once we disallow casting `*const dyn Trait + 'short`
+                                // to `*const dyn Trait + 'long`, then this can just be `src_lt`.
+                                dst_lt,
+                                ty::Dyn,
+                            );
+                            let dst_obj = Ty::new_dynamic(
+                                tcx,
+                                tcx.mk_poly_existential_predicates(
+                                    &dst_tty.without_auto_traits().collect::<Vec<_>>(),
+                                ),
+                                dst_lt,
+                                ty::Dyn,
+                            );
 
-                                    debug!(?src_tty, ?dst_tty, ?src_obj, ?dst_obj);
+                            debug!(?src_tty, ?dst_tty, ?src_obj, ?dst_obj);
 
-                                    self.sub_types(
-                                        src_obj,
-                                        dst_obj,
-                                        location.to_locations(),
-                                        ConstraintCategory::Cast {
-                                            is_implicit_coercion: false,
-                                            unsize_to: None,
-                                        },
-                                    )
-                                    .unwrap();
-                                }
-                            }
-                            _ => {
-                                span_mirbug!(
-                                    self,
-                                    rvalue,
-                                    "Invalid PtrToPtr cast {:?} -> {:?}",
-                                    ty_from,
-                                    ty
-                                )
-                            }
+                            self.sub_types(
+                                src_obj,
+                                dst_obj,
+                                location.to_locations(),
+                                ConstraintCategory::Cast {
+                                    is_implicit_coercion: false,
+                                    unsize_to: None,
+                                },
+                            )
+                            .unwrap();
                         }
                     }
                     CastKind::Transmute => {