diff --git a/Docs/src/flowcontrol.but b/Docs/src/flowcontrol.but
index f390584d..021d7a02 100644
--- a/Docs/src/flowcontrol.but
+++ b/Docs/src/flowcontrol.but
@@ -218,6 +218,8 @@ Displays a MessageBox containing the text "messagebox_text". mb_option_list must
 
 \b \e{MB_RIGHT} - Right align text
 
+\b \e{MB_RTLREADING} - RTL reading order
+
 \b \e{MB_DEFBUTTON1} - Button 1 is default
 
 \b \e{MB_DEFBUTTON2} - Button 2 is default
diff --git a/Source/script.cpp b/Source/script.cpp
index d2fb9f75..a91bb33f 100644
--- a/Source/script.cpp
+++ b/Source/script.cpp
@@ -3519,6 +3519,7 @@ int CEXEBuild::doCommand(int which_token, LineParser &line)
           MBD(MB_TOPMOST)
           MBD(MB_SETFOREGROUND)
           MBD(MB_RIGHT)
+          MBD(MB_RTLREADING)
           MBD(MB_DEFBUTTON1)
           MBD(MB_DEFBUTTON2)
           MBD(MB_DEFBUTTON3)