diff --git a/Koha/Patron.pm b/Koha/Patron.pm
index ecfe7d40bb..203fa212c3 100644
--- a/Koha/Patron.pm
+++ b/Koha/Patron.pm
@@ -388,7 +388,7 @@ sub store {
 
                 if (    C4::Context->preference('ChildNeedsGuarantor')
                     and ( $self->is_child or $self->category->can_be_guarantee )
-                    and $self->contactname eq ""
+                    and ( !defined $self->contactname || $self->contactname eq "" )
                     and !@$guarantors )
                 {
                     Koha::Exceptions::Patron::Relationship::NoGuarantor->throw();
diff --git a/t/db_dependent/Letters.t b/t/db_dependent/Letters.t
index 4edf7c80f5..5cdf9b289d 100755
--- a/t/db_dependent/Letters.t
+++ b/t/db_dependent/Letters.t
@@ -19,7 +19,8 @@
 
 use Modern::Perl;
 use File::Basename qw(dirname);
-use Test::More tests => 104;
+use Test::More tests => 105;
+use Test::NoWarnings;
 
 use Test::MockModule;
 use Test::Warn;