diff --git a/compiler/file_output_stream.h b/compiler/file_output_stream.h
index bde9e68..76b00fe 100644
--- a/compiler/file_output_stream.h
+++ b/compiler/file_output_stream.h
@@ -29,7 +29,7 @@
 
   virtual ~FileOutputStream() {}
 
-  virtual bool WriteFully(const void* buffer, int64_t byte_count);
+  virtual bool WriteFully(const void* buffer, size_t byte_count);
 
   virtual off_t Seek(off_t offset, Whence whence);