diff --git a/installer/data/mysql/db_revs/220600048.pl b/installer/data/mysql/db_revs/220600048.pl
index 8fb5e9c322..7f59d65996 100755
--- a/installer/data/mysql/db_revs/220600048.pl
+++ b/installer/data/mysql/db_revs/220600048.pl
@@ -1,18 +1,23 @@
 use Modern::Perl;
 
 return {
-    bug_number => 30472,
+    bug_number => 30472, # adjusted on bug 33671
     description => "borrower_relationships.guarantor_id NOT NULL",
     up => sub {
         my ($args) = @_;
         my ($dbh, $out) = @$args{qw(dbh out)};
 
-        # Delete 'empty' guarantors. No longer possible to add them via interface. Have no use.
-        $dbh->do(q{
-DELETE FROM borrower_relationships WHERE guarantor_id IS NULL
+        # Delete bad/empty guarantors. No longer possible to add them via interface. Have no use.
+        my $cnt = $dbh->do(q{
+DELETE borrower_relationships FROM borrower_relationships LEFT JOIN borrowers bo ON bo.borrowernumber=guarantor_id WHERE guarantor_id IS NULL OR bo.borrowernumber IS NULL;
         });
+        say $out "Removed $cnt bad guarantor relationship records" if $cnt && $cnt =~ /^\d+$/;
+
+        # Make column NOT NULL, disable FK checks while doing so
+        $dbh->do('SET FOREIGN_KEY_CHECKS=0');
         $dbh->do(q{
 ALTER TABLE borrower_relationships CHANGE COLUMN guarantor_id guarantor_id int(11) NOT NULL
         });
+        $dbh->do('SET FOREIGN_KEY_CHECKS=1');
     },
 };