diff -uNr chemtool-1.6.11/main.c chemtool-1.6.11-new/main.c
--- chemtool-1.6.11/main.c	2007-08-26 14:49:26 +0300
+++ chemtool-1.6.11-new/main.c	2008-05-11 15:00:28 +0300
@@ -2950,6 +2950,10 @@
   strcpy (oldname, filename);
   strcpy (filename,
 	  gtk_file_selection_get_filename (GTK_FILE_SELECTION (fs)));
+  
+  if (strstr(filename, ".cht") == NULL)    
+    strcat(filename, ".cht");
+	  
   if (datadir == NULL || (int)strlen (datadir) == 0)
     {
       tempstr = strrchr (filename, '/');