diff --git a/openquake/hazardlib/source/multi_fault.py b/openquake/hazardlib/source/multi_fault.py
index d35ff4a8e11..b5df60c96e3 100644
--- a/openquake/hazardlib/source/multi_fault.py
+++ b/openquake/hazardlib/source/multi_fault.py
@@ -276,7 +276,7 @@ def _set_rupids_by_tag(src, allrids, dists, s2i):
     for tag, idxs in src.faults.items():
         fids = U32([s2i[idx] for idx in idxs])
         rid = np.argmin(dists[fids])
-        closest.append((dists[rid], tag, fids))
+        closest.append((dists[fids][rid], tag, fids))
 
     # build dictionary src.rupids_by_tag with the indices of
     # ruptures belonging to each fault source; care is taken
@@ -301,6 +301,7 @@ def _set_rupids_by_tag(src, allrids, dists, s2i):
         src.rupids_by_tag['off_rupids'] = off_rupids
 
 
+
 # NB: as side effect delete _rupture_idxs,
 # add .hdf5path and possibly .rupids_by_tag
 def save_and_split(mfsources, sectiondict, hdf5path, site1=None,