Index: guild.c
===================================================================
--- guild.c	(revision 16244)
+++ guild.c	(working copy)
@@ -623,6 +623,13 @@
 		return 0;
 	}
 
+	ARR_FIND( 0, g->max_member, i, g->member[i].class_ != tsd->status.class_ );
+	if(i)
+	{
+		clif_colormes(sd, COLOR_RED, "Your Guild already has this class");
+		return 0;
+	}
+
 	tsd->guild_invite=sd->status.guild_id;
 	tsd->guild_invite_account=sd->status.account_id;