diff --git a/src/objects-inl.h b/src/objects-inl.h
index 57fc2a056b..f26f4c220b 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -5288,7 +5288,7 @@ BOOL_ACCESSORS(JSPromise, flags, handled_hint, kHandledHintBit)
 ACCESSORS(JSRegExp, data, Object, kDataOffset)
 ACCESSORS(JSRegExp, flags, Object, kFlagsOffset)
 ACCESSORS(JSRegExp, source, Object, kSourceOffset)
-
+ACCESSORS(JSRegExp, last_index, Object, kLastIndexOffset)
 
 JSRegExp::Type JSRegExp::TypeTag() {
   Object* data = this->data();
@@ -5345,19 +5345,6 @@ void JSRegExp::SetDataAt(int index, Object* value) {
   FixedArray::cast(data())->set(index, value);
 }
 
-void JSRegExp::SetLastIndex(int index) {
-  static const int offset =
-      kSize + JSRegExp::kLastIndexFieldIndex * kPointerSize;
-  Smi* value = Smi::FromInt(index);
-  WRITE_FIELD(this, offset, value);
-}
-
-Object* JSRegExp::LastIndex() {
-  static const int offset =
-      kSize + JSRegExp::kLastIndexFieldIndex * kPointerSize;
-  return READ_FIELD(this, offset);
-}
-
 ElementsKind JSObject::GetElementsKind() {
   ElementsKind kind = map()->elements_kind();
 #if VERIFY_HEAP && DEBUG
diff --git a/src/objects.h b/src/objects.h
index beb903aff3..010bec7741 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -5697,6 +5697,7 @@ class JSRegExp: public JSObject {
 
   DECL_ACCESSORS(data, Object)
   DECL_ACCESSORS(flags, Object)
+  DECL_ACCESSORS(last_index, Object)
   DECL_ACCESSORS(source, Object)
 
   V8_EXPORT_PRIVATE static MaybeHandle<JSRegExp> New(Handle<String> source,
@@ -5719,9 +5720,6 @@ class JSRegExp: public JSObject {
   // Set implementation data after the object has been prepared.
   inline void SetDataAt(int index, Object* value);
 
-  inline void SetLastIndex(int index);
-  inline Object* LastIndex();
-
   static int code_index(bool is_latin1) {
     if (is_latin1) {
       return kIrregexpLatin1CodeIndex;
@@ -5740,6 +5738,7 @@ class JSRegExp: public JSObject {
   static const int kSourceOffset = kDataOffset + kPointerSize;
   static const int kFlagsOffset = kSourceOffset + kPointerSize;
   static const int kSize = kFlagsOffset + kPointerSize;
+  static const int kLastIndexOffset = kSize;  // In-object field.
 
   // Indices in the data array.
   static const int kTagIndex = 0;
diff --git a/src/regexp/regexp-utils.cc b/src/regexp/regexp-utils.cc
index 88ecb85dfa..b683db27f3 100644
--- a/src/regexp/regexp-utils.cc
+++ b/src/regexp/regexp-utils.cc
@@ -45,7 +45,8 @@ MaybeHandle<Object> RegExpUtils::SetLastIndex(Isolate* isolate,
                                               Handle<JSReceiver> recv,
                                               int value) {
   if (HasInitialRegExpMap(isolate, recv)) {
-    JSRegExp::cast(*recv)->SetLastIndex(value);
+    JSRegExp::cast(*recv)->set_last_index(Smi::FromInt(value),
+                                          SKIP_WRITE_BARRIER);
     return recv;
   } else {
     return Object::SetProperty(recv, isolate->factory()->lastIndex_string(),
@@ -56,7 +57,7 @@ MaybeHandle<Object> RegExpUtils::SetLastIndex(Isolate* isolate,
 MaybeHandle<Object> RegExpUtils::GetLastIndex(Isolate* isolate,
                                               Handle<JSReceiver> recv) {
   if (HasInitialRegExpMap(isolate, recv)) {
-    return handle(JSRegExp::cast(*recv)->LastIndex(), isolate);
+    return handle(JSRegExp::cast(*recv)->last_index(), isolate);
   } else {
     return Object::GetProperty(recv, isolate->factory()->lastIndex_string());
   }
@@ -151,7 +152,7 @@ bool RegExpUtils::IsUnmodifiedRegExp(Isolate* isolate, Handle<Object> obj) {
 
   // The smi check is required to omit ToLength(lastIndex) calls with possible
   // user-code execution on the fast path.
-  Object* last_index = JSRegExp::cast(recv)->LastIndex();
+  Object* last_index = JSRegExp::cast(recv)->last_index();
   return last_index->IsSmi() && Smi::ToInt(last_index) >= 0;
 }
 
diff --git a/src/runtime/runtime-regexp.cc b/src/runtime/runtime-regexp.cc
index a5d61d8348..968a1361f4 100644
--- a/src/runtime/runtime-regexp.cc
+++ b/src/runtime/runtime-regexp.cc
@@ -1352,7 +1352,7 @@ MUST_USE_RESULT MaybeHandle<String> RegExpReplace(Isolate* isolate,
 
     uint32_t last_index = 0;
     if (sticky) {
-      Handle<Object> last_index_obj(regexp->LastIndex(), isolate);
+      Handle<Object> last_index_obj(regexp->last_index(), isolate);
       ASSIGN_RETURN_ON_EXCEPTION(isolate, last_index_obj,
                                  Object::ToLength(isolate, last_index_obj),
                                  String);
@@ -1367,7 +1367,7 @@ MUST_USE_RESULT MaybeHandle<String> RegExpReplace(Isolate* isolate,
         RegExpImpl::Exec(regexp, string, last_index, last_match_info), String);
 
     if (match_indices_obj->IsNull(isolate)) {
-      if (sticky) regexp->SetLastIndex(0);
+      if (sticky) regexp->set_last_index(Smi::kZero, SKIP_WRITE_BARRIER);
       return string;
     }
 
@@ -1376,7 +1376,8 @@ MUST_USE_RESULT MaybeHandle<String> RegExpReplace(Isolate* isolate,
     const int start_index = match_indices->Capture(0);
     const int end_index = match_indices->Capture(1);
 
-    if (sticky) regexp->SetLastIndex(end_index);
+    if (sticky)
+      regexp->set_last_index(Smi::FromInt(end_index), SKIP_WRITE_BARRIER);
 
     IncrementalStringBuilder builder(isolate);
     builder.AppendString(factory->NewSubString(string, 0, start_index));
@@ -1471,7 +1472,7 @@ RUNTIME_FUNCTION(Runtime_StringReplaceNonGlobalRegExpWithFunction) {
   const bool sticky = (flags & JSRegExp::kSticky) != 0;
   uint32_t last_index = 0;
   if (sticky) {
-    Handle<Object> last_index_obj(regexp->LastIndex(), isolate);
+    Handle<Object> last_index_obj(regexp->last_index(), isolate);
     ASSIGN_RETURN_FAILURE_ON_EXCEPTION(
         isolate, last_index_obj, Object::ToLength(isolate, last_index_obj));
     last_index = PositiveNumberToUint32(*last_index_obj);
@@ -1485,7 +1486,7 @@ RUNTIME_FUNCTION(Runtime_StringReplaceNonGlobalRegExpWithFunction) {
       RegExpImpl::Exec(regexp, subject, last_index, last_match_info));
 
   if (match_indices_obj->IsNull(isolate)) {
-    if (sticky) regexp->SetLastIndex(0);
+    if (sticky) regexp->set_last_index(Smi::kZero, SKIP_WRITE_BARRIER);
     return *subject;
   }
 
@@ -1495,7 +1496,8 @@ RUNTIME_FUNCTION(Runtime_StringReplaceNonGlobalRegExpWithFunction) {
   const int index = match_indices->Capture(0);
   const int end_of_match = match_indices->Capture(1);
 
-  if (sticky) regexp->SetLastIndex(end_of_match);
+  if (sticky)
+    regexp->set_last_index(Smi::FromInt(end_of_match), SKIP_WRITE_BARRIER);
 
   IncrementalStringBuilder builder(isolate);
   builder.AppendString(factory->NewSubString(subject, 0, index));