Index: text_delta.c
===================================================================
--- text_delta.c	(revision 20792)
+++ text_delta.c	(working copy)
@@ -148,7 +148,8 @@ compute_window(const char *data, apr_siz
   build_baton.new_data = svn_stringbuf_create("", pool);
 
   if (source_len == 0)
-    svn_txdelta__vdelta(&build_baton, data, source_len, target_len, pool);
+    svn_txdelta__insert_op(&build_baton, svn_txdelta_new, 0, source_len,
+                           data, pool);
   else
     svn_txdelta__xdelta(&build_baton, data, source_len, target_len, pool);