diff --git a/mock_file_writer.h b/mock_file_writer.h
index 7cf0fd5..f2785cc 100644
--- a/mock_file_writer.h
+++ b/mock_file_writer.h
@@ -25,7 +25,7 @@
     return 0;
   }
 
-  virtual int Write(const void* bytes, size_t count) {
+  virtual ssize_t Write(const void* bytes, size_t count) {
     CHECK(was_opened_);
     CHECK(!was_closed_);
     const char* char_bytes = reinterpret_cast<const char*>(bytes);