diff --git a/modules/bibformat/lib/elements/bfe_references.py b/modules/bibformat/lib/elements/bfe_references.py
index 2fed3ee41..ed24925d4 100755
--- a/modules/bibformat/lib/elements/bfe_references.py
+++ b/modules/bibformat/lib/elements/bfe_references.py
@@ -1,70 +1,72 @@
 # -*- coding: utf-8 -*-
 """BibFormat element - Prints references"""
 import re
 
 from invenio.messages import gettext_set_language
 
 
 def format(bfo):
     """
     Print host (Order: Name of publisher, place of publication and date of publication).
 
     """
     _ = gettext_set_language(bfo.lang)
     output = []
     epflid = bfo.field('037__a', escape=2).strip()
     if epflid:
         output.append(epflid)
     
     doi = bfo.field('0247_a', escape=2).strip()
     if doi:
         doi_re = re.compile(r'(10.(\d)+/(\S)+)')
         if doi_re.search(doi):
             output.append('<a href="http://dx.doi.org/%s">doi:%s</a>' % (doi, doi))
             
     # show patent search ?
     if bfo.field('013__a'):
         if bfo.lang == 'fr':
             url = "http://worldwide.espacenet.com/searchResults?compact=false&PN=%s&ST=advanced&locale=fr_EP&DB=EPODOC" % str(bfo.field('013__a', escape=2))
         else:
             url = "http://worldwide.espacenet.com/searchResults?compact=false&PN=%s&ST=advanced&locale=en_EP&DB=EPODOC" % str(bfo.field('013__a', escape=2))
         output.append('<a href="%s" target="_blank">%s</a>' % (url, _("Search for this record at the European Patent Office")))
 
     external = bfo.fields('035__a')
     control_nb_re = re.compile(r'(?P<id>[\w:_,.\-_/]+)\s*\((?P<cataloger>[a-z\s]+)\)', re.I)
     for ext in external:
         match = control_nb_re.match(ext)
         if match:
             extra_id = match.group('id')
             cataloger = match.group('cataloger')
-        if cataloger == 'ISI':
-            url = 'http://ws.isiknowledge.com/cps/openurl/service?url_ver=Z39.88-2004&amp;rft_id=info:ut/%s' % extra_id
-            output.append('<a href="%s">%s</a>' % (url, _("View record in Web of Science")))
-        elif cataloger == 'Scopus':
-            url = 'http://www.scopus.com/scopus/openurl/link.url?ctx_ver=Z39.88-2004&amp;rfr_id=http://infoscience.epfl.ch&amp;rft_id=info:eid/%s' % extra_id
-            output.append('<a href="%s">%s</a>' % (url, _("View record in Scopus")))
-        elif cataloger == 'PMID':
-            url = 'http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=%s&dopt=Abstract' % extra_id
-            output.append('<a href="%s">%s</a>' % (url, _("View record in PubMed")))
-        elif cataloger == 'arXiv':
-            url = 'http://www.arxiv.org/openurl-resolver?rft_id=%s&amp;url_ver=Z39.88-2004' % extra_id
-            output.append('<a href="%s">%s</a>' % (url, _("View record in arXiv")))
-        elif cataloger == 'EV':
-            pass
-        elif cataloger == 'SzZuIDS NEBIS':
-            if bfo.lang == 'fr':
-                url = 'http://library.epfl.ch/nebis-redir/?record=%s' % extra_id
-            else:
-                url = 'http://library.epfl.ch/en/nebis-redir/?record=%s' % extra_id
-            
-            output.append('<a href="%s">%s</a>' % (url, _("Print copy in library catalog")))
+
+            if extra_id and cataloger:
+                if cataloger == 'ISI':
+                    url = 'http://ws.isiknowledge.com/cps/openurl/service?url_ver=Z39.88-2004&amp;rft_id=info:ut/%s' % extra_id
+                    output.append('<a href="%s">%s</a>' % (url, _("View record in Web of Science")))
+                elif cataloger == 'Scopus':
+                    url = 'http://www.scopus.com/scopus/openurl/link.url?ctx_ver=Z39.88-2004&amp;rfr_id=http://infoscience.epfl.ch&amp;rft_id=info:eid/%s' % extra_id
+                    output.append('<a href="%s">%s</a>' % (url, _("View record in Scopus")))
+                elif cataloger == 'PMID':
+                    url = 'http://www.ncbi.nlm.nih.gov/sites/entrez?cmd=Retrieve&db=PubMed&list_uids=%s&dopt=Abstract' % extra_id
+                    output.append('<a href="%s">%s</a>' % (url, _("View record in PubMed")))
+                elif cataloger == 'arXiv':
+                    url = 'http://www.arxiv.org/openurl-resolver?rft_id=%s&amp;url_ver=Z39.88-2004' % extra_id
+                    output.append('<a href="%s">%s</a>' % (url, _("View record in arXiv")))
+                elif cataloger == 'EV':
+                    pass
+                elif cataloger == 'SzZuIDS NEBIS':
+                    if bfo.lang == 'fr':
+                        url = 'http://library.epfl.ch/nebis-redir/?record=%s' % extra_id
+                    else:
+                        url = 'http://library.epfl.ch/en/nebis-redir/?record=%s' % extra_id
+
+                    output.append('<a href="%s">%s</a>' % (url, _("Print copy in library catalog")))
         
         
     return ''.join(['<li>%s</li>' % elem for elem in output])
 
 def escape_values(bfo):
     """
     Called by BibFormat in order to check if output of this element
     should be escaped.
     """
     return 0