diff --git a/vncviewer/Surface.h b/vncviewer/Surface.h
index 7d16468..032889b 100644
--- a/vncviewer/Surface.h
+++ b/vncviewer/Surface.h
@@ -44,8 +44,8 @@
   void draw(int src_x, int src_y, int x, int y, int w, int h);
   void draw(Surface* dst, int src_x, int src_y, int x, int y, int w, int h);
 
-  void blend(int src_x, int src_y, int x, int y, int w, int h);
-  void blend(Surface* dst, int src_x, int src_y, int x, int y, int w, int h);
+  void blend(int src_x, int src_y, int x, int y, int w, int h, int a=255);
+  void blend(Surface* dst, int src_x, int src_y, int x, int y, int w, int h, int a=255);
 
 protected:
   void alloc();