def fix_dendrogram(graph, cl):
    already_merged = set()
    for merge in cl.merges:
        already_merged.update(merge)

    num_dendrogram_nodes = graph.vcount() + len(cl.merges)
    not_merged_yet = sorted(set(xrange(num_dendrogram_nodes)) - already_merged)
    if len(not_merged_yet) < 2:
        return

    v1, v2 = not_merged_yet[:2]
    cl._merges.append((v1, v2))
    del not_merged_yet[:2]

    missing_nodes = xrange(num_dendrogram_nodes,
            num_dendrogram_nodes + len(not_merged_yet))
    cl._merges.extend(izip(not_merged_yet, missing_nodes))
    cl._nmerges = graph.vcount()-1