diff --git a/include/v8.h b/include/v8.h
index c24445f0d9..eb1f08a609 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -7870,6 +7870,11 @@ class V8_EXPORT ExtensionConfiguration {
   const char** names_;
 };
 
+#ifndef V8_CONTEXT_PROXY_INTERNAL_FIELD_COUNT
+// The number of required internal fields for global proxy objects can be
+// defined by embedder.
+#define V8_CONTEXT_PROXY_INTERNAL_FIELD_COUNT 2
+#endif
 
 /**
  * A sandboxed execution context with its own set of built-in objects
@@ -8068,6 +8073,9 @@ class V8_EXPORT Context {
     Local<Context> context_;
   };
 
+  static const int kProxyInternalFieldCount =
+      V8_CONTEXT_PROXY_INTERNAL_FIELD_COUNT;
+
  private:
   friend class Value;
   friend class Script;
diff --git a/src/api-natives.cc b/src/api-natives.cc
index ab1b06256e..5a78003140 100644
--- a/src/api-natives.cc
+++ b/src/api-natives.cc
@@ -641,6 +641,7 @@ Handle<JSFunction> ApiNatives::CreateApiFunction(
     case GlobalProxyType:
       type = JS_GLOBAL_PROXY_TYPE;
       instance_size += JSGlobalProxy::kSize;
+      DCHECK_EQ(instance_size, JSGlobalProxy::kSizeWithInternalFields);
       break;
     default:
       UNREACHABLE();
diff --git a/src/api.cc b/src/api.cc
index ad41d819b7..b7a5b2e4ec 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -6075,6 +6075,9 @@ static i::Handle<ObjectType> CreateEnvironment(
       proxy_constructor->set_prototype_template(
           *Utils::OpenHandle(*global_template));
 
+      proxy_template->SetInternalFieldCount(
+          v8::Context::kProxyInternalFieldCount);
+
       // Migrate security handlers from global_template to
       // proxy_template.  Temporarily removing access check
       // information from the global template.
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index a4cb79d546..e484c80203 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -960,8 +960,9 @@ Handle<JSGlobalObject> Genesis::CreateNewGlobals(
   if (global_proxy_template.IsEmpty()) {
     Handle<String> name = Handle<String>(heap()->empty_string());
     Handle<Code> code = isolate()->builtins()->Illegal();
-    global_proxy_function = factory()->NewFunction(
-        name, code, JS_GLOBAL_PROXY_TYPE, JSGlobalProxy::kSize);
+    global_proxy_function =
+        factory()->NewFunction(name, code, JS_GLOBAL_PROXY_TYPE,
+                               JSGlobalProxy::kSizeWithInternalFields);
   } else {
     Handle<ObjectTemplateInfo> data =
         v8::Utils::OpenHandle(*global_proxy_template);
@@ -4494,9 +4495,11 @@ Genesis::Genesis(Isolate* isolate,
   Handle<JSFunction> global_proxy_function =
       isolate->factory()->NewFunctionFromSharedFunctionInfo(
           initial_map, shared, factory()->undefined_value());
-  DCHECK_EQ(global_proxy_data->internal_field_count(), 0);
+  DCHECK_EQ(global_proxy_data->internal_field_count(),
+            v8::Context::kProxyInternalFieldCount);
   Handle<Map> global_proxy_map = isolate->factory()->NewMap(
-      JS_GLOBAL_PROXY_TYPE, JSGlobalProxy::kSize, FAST_HOLEY_SMI_ELEMENTS);
+      JS_GLOBAL_PROXY_TYPE, JSGlobalProxy::kSizeWithInternalFields,
+      FAST_HOLEY_SMI_ELEMENTS);
   JSFunction::SetInitialMap(global_proxy_function, global_proxy_map,
                             factory()->null_value());
   global_proxy_map->set_is_access_check_needed(true);
diff --git a/src/factory.cc b/src/factory.cc
index 4636030744..749188f6bf 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -2182,7 +2182,8 @@ Handle<JSProxy> Factory::NewJSProxy(Handle<JSReceiver> target,
 Handle<JSGlobalProxy> Factory::NewUninitializedJSGlobalProxy() {
   // Create an empty shell of a JSGlobalProxy that needs to be reinitialized
   // via ReinitializeJSGlobalProxy later.
-  Handle<Map> map = NewMap(JS_GLOBAL_PROXY_TYPE, JSGlobalProxy::kSize);
+  Handle<Map> map =
+      NewMap(JS_GLOBAL_PROXY_TYPE, JSGlobalProxy::kSizeWithInternalFields);
   // Maintain invariant expected from any JSGlobalProxy.
   map->set_is_access_check_needed(true);
   CALL_HEAP_FUNCTION(
diff --git a/src/objects.h b/src/objects.h
index 08e1e568a2..9e3c0372ce 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -8512,6 +8512,8 @@ class JSGlobalProxy : public JSObject {
   static const int kNativeContextOffset = JSObject::kHeaderSize;
   static const int kHashOffset = kNativeContextOffset + kPointerSize;
   static const int kSize = kHashOffset + kPointerSize;
+  static const int kSizeWithInternalFields =
+      kSize + v8::Context::kProxyInternalFieldCount * kPointerSize;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSGlobalProxy);
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index 7abfa99de6..ee202c2e99 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -25977,3 +25977,14 @@ THREADED_TEST(ImmutableProtoWithParent) {
             ->Equals(context.local(), original_proto)
             .FromJust());
 }
+
+TEST(InternalFieldsOnGlobalProxy) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope scope(isolate);
+
+  v8::Local<v8::ObjectTemplate> obj_template = v8::ObjectTemplate::New(isolate);
+
+  v8::Local<v8::Context> context = Context::New(isolate, nullptr, obj_template);
+  v8::Local<v8::Object> global = context->Global();
+  CHECK_EQ(v8::Context::kProxyInternalFieldCount, global->InternalFieldCount());
+}