diff --git a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
index 2c6c461267a..6fd67b07467 100644
--- a/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
+++ b/compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs
@@ -9,10 +9,7 @@ use rustc_middle::mir::{Mutability, Place, PlaceRef, ProjectionElem};
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use rustc_middle::{
     hir::place::PlaceBase,
-    mir::{
-        self, BindingForm, ClearCrossCrate, ImplicitSelfKind, Local, LocalDecl, LocalInfo,
-        LocalKind, Location,
-    },
+    mir::{self, BindingForm, ClearCrossCrate, Local, LocalDecl, LocalInfo, LocalKind, Location},
 };
 use rustc_span::source_map::DesugaringKind;
 use rustc_span::symbol::{kw, Symbol};
@@ -312,7 +309,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     && !matches!(
                         decl.local_info,
                         Some(box LocalInfo::User(ClearCrossCrate::Set(BindingForm::ImplicitSelf(
-                            ImplicitSelfKind::MutRef
+                            hir::ImplicitSelfKind::MutRef
                         ))))
                     )
                 {
@@ -1074,7 +1071,7 @@ fn mut_borrow_of_mutable_ref(local_decl: &LocalDecl<'_>, local_name: Option<Symb
             //
             // Deliberately fall into this case for all implicit self types,
             // so that we don't fall in to the next case with them.
-            *kind == mir::ImplicitSelfKind::MutRef
+            *kind == hir::ImplicitSelfKind::MutRef
         }
         _ if Some(kw::SelfLower) == local_name => {
             // Otherwise, check if the name is the `self` keyword - in which case
diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 1d62caef9b7..037cbc1be9a 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2661,7 +2661,7 @@ pub struct FnDecl<'hir> {
 }
 
 /// Represents what type of implicit self a function has, if any.
-#[derive(Copy, Clone, Encodable, Decodable, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub enum ImplicitSelfKind {
     /// Represents a `fn x(self);`.
     Imm,
diff --git a/compiler/rustc_middle/src/mir/mod.rs b/compiler/rustc_middle/src/mir/mod.rs
index dd768c5358d..9a6d34c8ddd 100644
--- a/compiler/rustc_middle/src/mir/mod.rs
+++ b/compiler/rustc_middle/src/mir/mod.rs
@@ -18,7 +18,7 @@ use rustc_data_structures::captures::Captures;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir::def::{CtorKind, Namespace};
 use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
-use rustc_hir::{self, GeneratorKind};
+use rustc_hir::{self, GeneratorKind, ImplicitSelfKind};
 use rustc_hir::{self as hir, HirId};
 use rustc_session::Session;
 use rustc_target::abi::{Size, VariantIdx};
@@ -653,22 +653,6 @@ pub enum BindingForm<'tcx> {
     RefForGuard,
 }
 
-/// Represents what type of implicit self a function has, if any.
-#[derive(Clone, Copy, PartialEq, Debug, TyEncodable, TyDecodable, HashStable)]
-pub enum ImplicitSelfKind {
-    /// Represents a `fn x(self);`.
-    Imm,
-    /// Represents a `fn x(mut self);`.
-    Mut,
-    /// Represents a `fn x(&self);`.
-    ImmRef,
-    /// Represents a `fn x(&mut self);`.
-    MutRef,
-    /// Represents when a function does not have a self argument or
-    /// when a function has a `self: X` argument.
-    None,
-}
-
 TrivialTypeTraversalAndLiftImpls! { BindingForm<'tcx>, }
 
 mod binding_form_impl {
diff --git a/compiler/rustc_mir_build/src/build/mod.rs b/compiler/rustc_mir_build/src/build/mod.rs
index 7d41969a314..0d8a2968ec0 100644
--- a/compiler/rustc_mir_build/src/build/mod.rs
+++ b/compiler/rustc_mir_build/src/build/mod.rs
@@ -11,7 +11,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
-use rustc_hir::{GeneratorKind, Node};
+use rustc_hir::{GeneratorKind, ImplicitSelfKind, Node};
 use rustc_index::vec::{Idx, IndexVec};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_middle::hir::place::PlaceBase as HirPlaceBase;
@@ -170,13 +170,7 @@ fn mir_build(tcx: TyCtxt<'_>, def: ty::WithOptConstParam<LocalDefId>) -> Body<'_
                         // Make sure that inferred closure args have no type span
                         .and_then(|ty| if arg.pat.span != ty.span { Some(ty.span) } else { None });
                     self_arg = if index == 0 && fn_decl.implicit_self.has_implicit_self() {
-                        match fn_decl.implicit_self {
-                            hir::ImplicitSelfKind::Imm => Some(ImplicitSelfKind::Imm),
-                            hir::ImplicitSelfKind::Mut => Some(ImplicitSelfKind::Mut),
-                            hir::ImplicitSelfKind::ImmRef => Some(ImplicitSelfKind::ImmRef),
-                            hir::ImplicitSelfKind::MutRef => Some(ImplicitSelfKind::MutRef),
-                            _ => None,
-                        }
+                        Some(fn_decl.implicit_self)
                     } else {
                         None
                     };
diff --git a/compiler/rustc_smir/src/mir.rs b/compiler/rustc_smir/src/mir.rs
index 855605b1a4f..887e6572930 100644
--- a/compiler/rustc_smir/src/mir.rs
+++ b/compiler/rustc_smir/src/mir.rs
@@ -1,10 +1,10 @@
+pub use crate::very_unstable::hir::ImplicitSelfKind;
 pub use crate::very_unstable::middle::mir::{
     visit::MutVisitor, AggregateKind, AssertKind, BasicBlock, BasicBlockData, BinOp, BindingForm,
     BlockTailInfo, Body, BorrowKind, CastKind, ClearCrossCrate, Constant, ConstantKind,
-    CopyNonOverlapping, Coverage, FakeReadCause, Field, GeneratorInfo, ImplicitSelfKind,
-    InlineAsmOperand, Local, LocalDecl, LocalInfo, LocalKind, Location, MirPhase, MirSource,
-    NullOp, Operand, Place, PlaceRef, ProjectionElem, ProjectionKind, Promoted, RetagKind, Rvalue,
-    Safety, SourceInfo, SourceScope, SourceScopeData, SourceScopeLocalData, Statement,
-    StatementKind, UnOp, UserTypeProjection, UserTypeProjections, VarBindingForm, VarDebugInfo,
-    VarDebugInfoContents,
+    CopyNonOverlapping, Coverage, FakeReadCause, Field, GeneratorInfo, InlineAsmOperand, Local,
+    LocalDecl, LocalInfo, LocalKind, Location, MirPhase, MirSource, NullOp, Operand, Place,
+    PlaceRef, ProjectionElem, ProjectionKind, Promoted, RetagKind, Rvalue, Safety, SourceInfo,
+    SourceScope, SourceScopeData, SourceScopeLocalData, Statement, StatementKind, UnOp,
+    UserTypeProjection, UserTypeProjections, VarBindingForm, VarDebugInfo, VarDebugInfoContents,
 };