--- src/mngutil.c.backup	2006-07-17 09:33:45.000000000 +0800
+++ src/mngutil.c	2006-07-17 09:39:15.000000000 +0800
@@ -30,12 +30,15 @@
 #include <png.h>
 #include "mngutil.h"
 
-extern void png_write_data (png_structp png_ptr,
-				png_bytep data,png_size_t length);
-extern void png_save_uint_32 (png_bytep buf, png_uint_32 i);
-extern void png_save_uint_16 (png_bytep buf, png_uint_16 i);
-extern void png_write_chunk (png_structp png_ptr,
-				png_bytep chunk_name, png_bytep data, png_size_t length);
+/* stolen from libpng */
+void /* PRIVATE */
+png_write_data(png_structp png_ptr, png_bytep data, png_size_t length)
+{
+   if (png_ptr->write_data_fn != NULL )
+      (*(png_ptr->write_data_fn))(png_ptr, data, length);
+   else
+      png_error(png_ptr, "Call to NULL write function");
+}
 
 png_byte mng_sig[8] = {138, 77, 78, 71, 13, 10, 26, 10};