diff --git a/serials/subscription-numberpatterns.pl b/serials/subscription-numberpatterns.pl
index a9bc998835..1669b4d66f 100755
--- a/serials/subscription-numberpatterns.pl
+++ b/serials/subscription-numberpatterns.pl
@@ -43,6 +43,12 @@ use C4::Serials::Numberpattern qw(
 );
 use C4::Serials::Frequency qw( GetSubscriptionFrequencies );
 
+my @NUMBERPATTERN_FIELDS = qw/
+      label description numberingmethod displayorder
+      label1 label2 label3 add1 add2 add3 every1 every2 every3
+      setto1 setto2 setto3 whenmorethan1 whenmorethan2 whenmorethan3
+      numbering1 numbering2 numbering3 /;
+
 my $input = CGI->new;
 my ($template, $loggedinuser, $cookie, $flags) = get_template_and_user( {
     template_name   => 'serials/subscription-numberpatterns.tt',
@@ -56,12 +62,9 @@ my $op = $input->param('op');
 if($op && $op eq 'savenew') {
     my $label = $input->param('label');
     my $numberpattern;
-    foreach(qw/ label description numberingmethod displayorder
-      label1 label2 label3 add1 add2 add3 every1 every2 every3
-      setto1 setto2 setto3 whenmorethan1 whenmorethan2 whenmorethan3
-      numbering1 numbering2 numbering3 /) {
+    foreach(@NUMBERPATTERN_FIELDS) {
         $numberpattern->{$_} = $input->param($_);
-        if($numberpattern->{$_} and $numberpattern->{$_} eq '') {
+        if(defined $numberpattern->{$_} and $numberpattern->{$_} eq '') {
             $numberpattern->{$_} = undef;
         }
     }
@@ -86,11 +89,11 @@ if($op && $op eq 'savenew') {
         }
     }
     if($mod_ok) {
-        foreach(qw/ id label description numberingmethod displayorder
-          label1 label2 label3 add1 add2 add3 every1 every2 every3
-          setto1 setto2 setto3 whenmorethan1 whenmorethan2 whenmorethan3
-          numbering1 numbering2 numbering3 /) {
+        foreach(@NUMBERPATTERN_FIELDS) {
             $numberpattern->{$_} = $input->param($_) || undef;
+            if(defined $numberpattern->{$_} and $numberpattern->{$_} eq '') {
+                $numberpattern->{$_} = undef;
+            }
         }
         ModSubscriptionNumberpattern($numberpattern);
     } else {