diff --git a/C4/Items.pm b/C4/Items.pm
index 5a7a56756f..ef38b67c24 100644
--- a/C4/Items.pm
+++ b/C4/Items.pm
@@ -1461,7 +1461,12 @@ sub get_hostitemnumbers_of {
 
     foreach my $hostfield ( $marcrecord->field($tag) ) {
         my $hostbiblionumber = $hostfield->subfield($biblio_s);
+        next unless $hostbiblionumber; # have tag, don't have $biblio_s subfield
         my $linkeditemnumber = $hostfield->subfield($item_s);
+        if ( ! $linkeditemnumber ) {
+            warn "ERROR biblionumber $biblionumber has 773^0, but doesn't have 9";
+            next;
+        }
         my @itemnumbers;
         if ( my $itemnumbers =
             get_itemnumbers_of($hostbiblionumber)->{$hostbiblionumber} )