problem with union and type in file.y

[Christian Fotsing]

Hi.
I work with Bison 2.3, and i have define my struct 
typedef
    struct RecChem {
        Instruction *Mot;
        int Nombre;
    } * Chemin;
in another file (extern.h).
In my Yacc file, i include extern.h, and declare 
%union{
    ------
    Chemin T_Chemin;
    ---------
}
When i compile, i have this error :

expected specifier-qualifier-list before ‘Chemin’

What can i do??

Sincerly..