diff --git a/doc/manual.xml b/doc/manual.xml
index 58d4941be6ee48156e404caf2fb2581cf7cc6db8..ea01f320efdb032c9f97ef82bda9cb498b5d5b15 100644
--- a/doc/manual.xml
+++ b/doc/manual.xml
@@ -3874,7 +3874,7 @@ plot_conditional_forecast(periods = 10) e u;
   <refsynopsisdiv>
     <cmdsynopsis>
       <command>plot_conditional_forecast</command>
-      <arg>(<option>periods</option> = <replaceable>INTEGER</replaceable>)</arg><arg choice="plain">;</arg>
+      <arg>(<option>periods</option> = <replaceable>INTEGER</replaceable>)</arg> <arg rep="repeat"><replaceable>VARIABLE_NAME</replaceable></arg><arg choice="plain">;</arg>
     </cmdsynopsis>
   </refsynopsisdiv>