diff --git a/test/fake_producer.h b/test/fake_producer.h
index 35149e3..622ed94 100644
--- a/test/fake_producer.h
+++ b/test/fake_producer.h
@@ -41,7 +41,7 @@
 
   // Produces a batch of events (as configured in the DataSourceConfig) and
   // posts a callback when the service acknowledges the commit.
-  void ProduceEventBatch(std::function<void()> callback);
+  void ProduceEventBatch(std::function<void()> callback = [] {});
 
   // Producer implementation.
   void OnConnect() override;
@@ -59,7 +59,7 @@
   base::TaskRunner* task_runner_ = nullptr;
   std::string name_;
   std::minstd_rand0 rnd_engine_;
-  uint32_t message_size_ = 0;
+  uint64_t message_size_ = 0;
   uint32_t message_count_ = 0;
   uint32_t max_messages_per_second_ = 0;
   std::function<void()> on_create_data_source_instance_;