diff --git a/docs/latex/wx/tex2rtf_css.ini b/docs/latex/wx/tex2rtf_css.ini
index d7a8a39529..d9a0bfcf60 100644
--- a/docs/latex/wx/tex2rtf_css.ini
+++ b/docs/latex/wx/tex2rtf_css.ini
@@ -54,6 +54,7 @@ htmlStylesheet = "wx.css"
 \arg [1] {{\it #1}}
 \true [0] {{\tt true}}
 \false [0] {{\tt false}}
+\NULL [0] {{\tt NULL}}
 
 ; make tex2rtf understand \hbox{} macro:
 \hbox [1] {#1}