diff --git a/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc b/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
index adddae83653..065159b7971 100644
--- a/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
+++ b/engine/src/flutter/lib/ui/window/platform_message_response_dart.cc
@@ -7,12 +7,41 @@
 #include <utility>
 
 #include "flutter/common/threads.h"
+#include "flutter/lib/ui/window/window.h"
 #include "lib/fxl/functional/make_copyable.h"
 #include "lib/tonic/dart_state.h"
 #include "lib/tonic/logging/dart_invoke.h"
 
 namespace blink {
 
+namespace {
+
+// Avoid copying the contents of messages beyond a certain size.
+const int kMessageCopyThreshold = 1000;
+
+void MessageDataFinalizer(void* isolate_callback_data,
+                          Dart_WeakPersistentHandle handle,
+                          void* peer) {
+  std::vector<uint8_t>* data = reinterpret_cast<std::vector<uint8_t>*>(peer);
+  delete data;
+}
+
+Dart_Handle WrapByteData(std::vector<uint8_t> data) {
+  if (data.size() < kMessageCopyThreshold) {
+    return ToByteData(data);
+  } else {
+    std::vector<uint8_t>* heap_data = new std::vector<uint8_t>(std::move(data));
+    Dart_Handle data_handle = Dart_NewExternalTypedData(
+        Dart_TypedData_kByteData, heap_data->data(), heap_data->size());
+    DART_CHECK_VALID(data_handle);
+    Dart_NewWeakPersistentHandle(data_handle, heap_data, heap_data->size(),
+                                 MessageDataFinalizer);
+    return data_handle;
+  }
+}
+
+}  // anonymous namespace
+
 PlatformMessageResponseDart::PlatformMessageResponseDart(
     tonic::DartPersistentValue callback)
     : callback_(std::move(callback)) {}
@@ -38,19 +67,7 @@ void PlatformMessageResponseDart::Complete(std::vector<uint8_t> data) {
           return;
         tonic::DartState::Scope scope(dart_state);
 
-        Dart_Handle byte_buffer =
-            Dart_NewTypedData(Dart_TypedData_kByteData, data.size());
-        DART_CHECK_VALID(byte_buffer);
-
-        void* buffer;
-        intptr_t length;
-        Dart_TypedData_Type type;
-        DART_CHECK_VALID(
-            Dart_TypedDataAcquireData(byte_buffer, &type, &buffer, &length));
-        FXL_CHECK(type == Dart_TypedData_kByteData);
-        FXL_CHECK(static_cast<size_t>(length) == data.size());
-        memcpy(buffer, data.data(), length);
-        Dart_TypedDataReleaseData(byte_buffer);
+        Dart_Handle byte_buffer = WrapByteData(std::move(data));
         tonic::DartInvoke(callback.Release(), {byte_buffer});
       }));
 }
diff --git a/engine/src/flutter/lib/ui/window/window.cc b/engine/src/flutter/lib/ui/window/window.cc
index 7b4cf2cde12..e12e03f10d0 100644
--- a/engine/src/flutter/lib/ui/window/window.cc
+++ b/engine/src/flutter/lib/ui/window/window.cc
@@ -22,23 +22,6 @@ using tonic::ToDart;
 namespace blink {
 namespace {
 
-Dart_Handle ToByteData(const std::vector<uint8_t>& buffer) {
-  Dart_Handle data_handle =
-      Dart_NewTypedData(Dart_TypedData_kByteData, buffer.size());
-  if (Dart_IsError(data_handle))
-    return data_handle;
-
-  Dart_TypedData_Type type;
-  void* data = nullptr;
-  intptr_t num_bytes = 0;
-  FXL_CHECK(!Dart_IsError(
-      Dart_TypedDataAcquireData(data_handle, &type, &data, &num_bytes)));
-
-  memcpy(data, buffer.data(), num_bytes);
-  Dart_TypedDataReleaseData(data_handle);
-  return data_handle;
-}
-
 void DefaultRouteName(Dart_NativeArguments args) {
   std::string routeName =
       UIDartState::Current()->window()->client()->DefaultRouteName();
@@ -119,6 +102,23 @@ void _RespondToPlatformMessage(Dart_NativeArguments args) {
 
 }  // namespace
 
+Dart_Handle ToByteData(const std::vector<uint8_t>& buffer) {
+  Dart_Handle data_handle =
+      Dart_NewTypedData(Dart_TypedData_kByteData, buffer.size());
+  if (Dart_IsError(data_handle))
+    return data_handle;
+
+  Dart_TypedData_Type type;
+  void* data = nullptr;
+  intptr_t num_bytes = 0;
+  FXL_CHECK(!Dart_IsError(
+      Dart_TypedDataAcquireData(data_handle, &type, &data, &num_bytes)));
+
+  memcpy(data, buffer.data(), num_bytes);
+  Dart_TypedDataReleaseData(data_handle);
+  return data_handle;
+}
+
 WindowClient::~WindowClient() {}
 
 Window::Window(WindowClient* client) : client_(client) {}
diff --git a/engine/src/flutter/lib/ui/window/window.h b/engine/src/flutter/lib/ui/window/window.h
index fa8ce41835b..ef0d7ef863a 100644
--- a/engine/src/flutter/lib/ui/window/window.h
+++ b/engine/src/flutter/lib/ui/window/window.h
@@ -21,6 +21,8 @@ class DartLibraryNatives;
 namespace blink {
 class Scene;
 
+Dart_Handle ToByteData(const std::vector<uint8_t>& buffer);
+
 class WindowClient {
  public:
   virtual std::string DefaultRouteName() = 0;