[Vala] Can adding new virtual method break ABI?

[Tal Hadad <tal_hd hotmail com>]

I've read how GObject define virtual methods, in the XClass struct, and
I'm afraid defining new virtual method can break ABI. Am I right?
Before:
struct _XClass
{
GObjectClass parent_class;

/* stuff */
void (*do_action) (X *self, /* parameters */);
};

After:
struct _XClass
{

GObjectClass parent_class;


/* stuff */


void (*another_action) (X *self, /* parameters */);

void (*do_action) (X *self, /* parameters */);

};

Can this case break ABI?

Tal