diff --git a/lib/ui/window/platform_message_response_dart.cc b/lib/ui/window/platform_message_response_dart.cc
index 702abad8d72bc..aed8f256cfba0 100644
--- a/lib/ui/window/platform_message_response_dart.cc
+++ b/lib/ui/window/platform_message_response_dart.cc
@@ -49,9 +49,10 @@ void PlatformMessageResponseDart::Complete(std::unique_ptr<fml::Mapping> data) {
         tonic::DartState::Scope scope(dart_state);
 
         void* mapping = data->GetMutableMapping();
+        size_t data_size = data->GetSize();
         Dart_Handle byte_buffer;
-        if (mapping) {
-          size_t data_size = data->GetSize();
+        if (mapping &&
+            data_size >= tonic::DartByteData::kExternalSizeThreshold) {
           byte_buffer = Dart_NewExternalTypedDataWithFinalizer(
               /*type=*/Dart_TypedData_kByteData,
               /*data=*/mapping,
diff --git a/third_party/tonic/typed_data/dart_byte_data.cc b/third_party/tonic/typed_data/dart_byte_data.cc
index cab038d14f85d..f4a557f17e946 100644
--- a/third_party/tonic/typed_data/dart_byte_data.cc
+++ b/third_party/tonic/typed_data/dart_byte_data.cc
@@ -11,17 +11,15 @@
 namespace tonic {
 
 namespace {
-
-// For large objects it is more efficient to use an external typed data object
-// with a buffer allocated outside the Dart heap.
-const int kExternalSizeThreshold = 1000;
-
 void FreeFinalizer(void* isolate_callback_data, void* peer) {
   free(peer);
 }
-
 }  // anonymous namespace
 
+// For large objects it is more efficient to use an external typed data object
+// with a buffer allocated outside the Dart heap.
+const size_t DartByteData::kExternalSizeThreshold = 1000;
+
 Dart_Handle DartByteData::Create(const void* data, size_t length) {
   if (length < kExternalSizeThreshold) {
     auto handle = DartByteData{data, length}.dart_handle();
diff --git a/third_party/tonic/typed_data/dart_byte_data.h b/third_party/tonic/typed_data/dart_byte_data.h
index bad96446de6f8..025df77dd0869 100644
--- a/third_party/tonic/typed_data/dart_byte_data.h
+++ b/third_party/tonic/typed_data/dart_byte_data.h
@@ -14,6 +14,7 @@ namespace tonic {
 
 class DartByteData {
  public:
+  static const size_t kExternalSizeThreshold;
   static Dart_Handle Create(const void* data, size_t length);
 
   explicit DartByteData(Dart_Handle list);