diff --git a/source/coral/files.cpp b/source/coral/files.cpp
index 312df0b..1d059b6 100644
--- a/source/coral/files.cpp
+++ b/source/coral/files.cpp
@@ -111,7 +111,9 @@ export namespace coral {
 	};
 
 	struct file_writer : public writer {
+		virtual expected<u64, io_error> seek(u64 offset) = 0;
 
+		virtual expected<u64, io_error> tell() = 0;
 	};
 
 	/**