diff --git a/plugins/mathview/itex2mml/itex2MML.y b/plugins/mathview/itex2mml/itex2MML.y
index c4e1cc5..60bc842 100644
--- a/plugins/mathview/itex2mml/itex2MML.y
+++ b/plugins/mathview/itex2mml/itex2MML.y
@@ -1804,6 +1804,7 @@ static void itex2MML_keep_error (const char * msg)
   itex2MML_last_error = itex2MML_copy_escaped (msg);
 }
 
+int itex2MML_do_html_filter (const char *, unsigned long, const int);
 int itex2MML_html_filter (const char * buffer, unsigned long length)
 {
   return itex2MML_do_html_filter (buffer, length, 0);