diff --git a/include/v8.h b/include/v8.h
index 1819943580..9fca8763d6 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -3816,7 +3816,7 @@ class Internals {
   static const int kFullStringRepresentationMask = 0x07;
   static const int kExternalTwoByteRepresentationTag = 0x02;
 
-  static const int kJSObjectType = 0xa6;
+  static const int kJSObjectType = 0xa7;
   static const int kFirstNonstringType = 0x80;
   static const int kForeignType = 0x85;
 
diff --git a/src/objects.cc b/src/objects.cc
index 61404b1a84..3041e5a5b9 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -4606,14 +4606,15 @@ MaybeObject* JSObject::DefineAccessor(String* name,
                                                  fun, attributes);
   }
 
-  AccessorPair* accessors;
+  Object* accessors;
   { MaybeObject* maybe_accessors = DefineGetterSetter(name, attributes);
-    if (!maybe_accessors->To<AccessorPair>(&accessors)) return maybe_accessors;
+    if (!maybe_accessors->To<Object>(&accessors)) return maybe_accessors;
   }
+  if (accessors->IsUndefined()) return accessors;
   if (is_getter) {
-    accessors->set_getter(fun);
+    AccessorPair::cast(accessors)->set_getter(fun);
   } else {
-    accessors->set_setter(fun);
+    AccessorPair::cast(accessors)->set_setter(fun);
   }
   return this;
 }
diff --git a/tools/grokdump.py b/tools/grokdump.py
index 44f9518f63..9977289872 100755
--- a/tools/grokdump.py
+++ b/tools/grokdump.py
@@ -506,10 +506,10 @@ class MinidumpReader(object):
 
 # List of V8 instance types. Obtained by adding the code below to any .cc file.
 #
-# #define DUMP_TYPE(T) printf("%d: \"%s\",\n", T, #T);
+# #define DUMP_TYPE(T) printf("  %d: \"%s\",\n", T, #T);
 # struct P {
 #   P() {
-#     printf("{\n");
+#     printf("INSTANCE_TYPES = {\n");
 #     INSTANCE_TYPE_LIST(DUMP_TYPE)
 #     printf("}\n");
 #   }
@@ -556,34 +556,35 @@ INSTANCE_TYPES = {
   144: "EXTERNAL_PIXEL_ARRAY_TYPE",
   146: "FILLER_TYPE",
   147: "ACCESSOR_INFO_TYPE",
-  148: "ACCESS_CHECK_INFO_TYPE",
-  149: "INTERCEPTOR_INFO_TYPE",
-  150: "CALL_HANDLER_INFO_TYPE",
-  151: "FUNCTION_TEMPLATE_INFO_TYPE",
-  152: "OBJECT_TEMPLATE_INFO_TYPE",
-  153: "SIGNATURE_INFO_TYPE",
-  154: "TYPE_SWITCH_INFO_TYPE",
-  155: "SCRIPT_TYPE",
-  156: "CODE_CACHE_TYPE",
-  157: "POLYMORPHIC_CODE_CACHE_TYPE",
-  160: "FIXED_ARRAY_TYPE",
+  148: "ACCESSOR_PAIR_TYPE",
+  149: "ACCESS_CHECK_INFO_TYPE",
+  150: "INTERCEPTOR_INFO_TYPE",
+  151: "CALL_HANDLER_INFO_TYPE",
+  152: "FUNCTION_TEMPLATE_INFO_TYPE",
+  153: "OBJECT_TEMPLATE_INFO_TYPE",
+  154: "SIGNATURE_INFO_TYPE",
+  155: "TYPE_SWITCH_INFO_TYPE",
+  156: "SCRIPT_TYPE",
+  157: "CODE_CACHE_TYPE",
+  158: "POLYMORPHIC_CODE_CACHE_TYPE",
+  161: "FIXED_ARRAY_TYPE",
   145: "FIXED_DOUBLE_ARRAY_TYPE",
-  161: "SHARED_FUNCTION_INFO_TYPE",
-  162: "JS_MESSAGE_OBJECT_TYPE",
-  165: "JS_VALUE_TYPE",
-  166: "JS_OBJECT_TYPE",
-  167: "JS_CONTEXT_EXTENSION_OBJECT_TYPE",
-  168: "JS_GLOBAL_OBJECT_TYPE",
-  169: "JS_BUILTINS_OBJECT_TYPE",
-  170: "JS_GLOBAL_PROXY_TYPE",
-  171: "JS_ARRAY_TYPE",
-  164: "JS_PROXY_TYPE",
-  174: "JS_WEAK_MAP_TYPE",
-  175: "JS_REGEXP_TYPE",
-  176: "JS_FUNCTION_TYPE",
-  163: "JS_FUNCTION_PROXY_TYPE",
-  158: "DEBUG_INFO_TYPE",
-  159: "BREAK_POINT_INFO_TYPE",
+  162: "SHARED_FUNCTION_INFO_TYPE",
+  163: "JS_MESSAGE_OBJECT_TYPE",
+  166: "JS_VALUE_TYPE",
+  167: "JS_OBJECT_TYPE",
+  168: "JS_CONTEXT_EXTENSION_OBJECT_TYPE",
+  169: "JS_GLOBAL_OBJECT_TYPE",
+  170: "JS_BUILTINS_OBJECT_TYPE",
+  171: "JS_GLOBAL_PROXY_TYPE",
+  172: "JS_ARRAY_TYPE",
+  165: "JS_PROXY_TYPE",
+  175: "JS_WEAK_MAP_TYPE",
+  176: "JS_REGEXP_TYPE",
+  177: "JS_FUNCTION_TYPE",
+  164: "JS_FUNCTION_PROXY_TYPE",
+  159: "DEBUG_INFO_TYPE",
+  160: "BREAK_POINT_INFO_TYPE",
 }