diff --git a/installer/data/mysql/atomicupdate/bug19096.perl b/installer/data/mysql/atomicupdate/bug19096.perl
new file mode 100644
index 0000000000..c392fd6b04
--- /dev/null
+++ b/installer/data/mysql/atomicupdate/bug19096.perl
@@ -0,0 +1,94 @@
+$DBversion = 'XXX';  # will be replaced by the RM
+if( CheckVersion( $DBversion ) ) {
+
+    my $dbh = C4::Context->dbh;
+
+    my $msss = $dbh->selectall_arrayref(q|
+        SELECT kohafield, tagfield, tagsubfield, frameworkcode
+        FROM marc_subfield_structure
+        WHERE   frameworkcode != ''
+    |, { Slice => {} });
+
+
+    my $sth = $dbh->prepare(q|
+        SELECT kohafield
+        FROM marc_subfield_structure
+        WHERE frameworkcode = ''
+        AND tagfield = ?
+        AND tagsubfield = ?
+    |);
+
+    my @exceptions;
+    for my $mss ( @$msss ) {
+        $sth->execute($mss->{tagfield}, $mss->{tagsubfield} );
+        my ( $default_kohafield ) = $sth->fetchrow_array();
+        if( $mss->{kohafield} ) {
+            push @exceptions, { frameworkcode => $mss->{frameworkcode}, tagfield => $mss->{tagfield}, tagsubfield => $mss->{tagsubfield}, kohafield => $mss->{kohafield} } if not $default_kohafield or $default_kohafield ne $mss->{kohafield};
+        } else {
+            push @exceptions, { frameworkcode => $mss->{frameworkcode}, tagfield => $mss->{tagfield}, tagsubfield => $mss->{tagsubfield}, kohafield => q{} } if $default_kohafield;
+        }
+    }
+
+    if (@exceptions) {
+        print
+"WARNING: The Default framework is now considered as authoritative for Koha to MARC mappings. We have found that your additional frameworks contained "
+          . scalar(@exceptions)
+          . " mapping(s) that deviate from the standard mappings. Please look at the following list and consider if you need to add them again in Default (possibly as a second mapping).\n";
+        for my $exception (@exceptions) {
+            print "Field "
+              . $exception->{tagfield} . '$'
+              . $exception->{tagsubfield}
+              . " in framework "
+              . $exception->{frameworkcode} . ': ';
+            if ( $exception->{kohafield} ) {
+                print "Mapping to "
+                  . $exception->{kohafield}
+                  . " has been adjusted.\n";
+            }
+            else {
+                print "Mapping has been reset.\n";
+            }
+        }
+
+        # Sync kohafield
+
+        # Clear the destination frameworks first
+        $dbh->do(q|
+            UPDATE marc_subfield_structure
+            SET kohafield = NULL
+            WHERE   frameworkcode > ''
+                AND     Kohafield > ''
+        |);
+
+        # Now copy from Default
+        my $msss = $dbh->selectall_arrayref(q|
+            SELECT kohafield, tagfield, tagsubfield
+            FROM marc_subfield_structure
+            WHERE   frameworkcode = ''
+                AND     kohafield > ''
+        |, { Slice => {} });
+        my $sth = $dbh->prepare(q|
+            UPDATE marc_subfield_structure
+            SET kohafield = ?
+            WHERE frameworkcode > ''
+            AND tagfield = ?
+            AND tagsubfield = ?
+        |);
+        for my $mss (@$msss) {
+            $sth->execute( $mss->{kohafield}, $mss->{tagfield},
+                $mss->{tagsubfield} );
+        }
+
+        # Clear the cache
+        my @frameworkcodes = $dbh->selectall_arrayref(q|
+            SELECT frameworkcode FROM biblio_framework WHERE frameworkcode > ''
+        |);
+        for my $frameworkcode (@frameworkcodes) {
+            Koha::Caches->get_instance->clear_from_cache("MarcSubfieldStructure-$frameworkcode");
+        }
+        Koha::Caches->get_instance->clear_from_cache("default_value_for_mod_marc-");
+    }
+
+    SetVersion( $DBversion );
+    print "Upgrade to $DBversion done (Bug 19096 - Make Default authoritative for Koha to MARC mappings)\n";
+}
diff --git a/t/db_dependent/Koha/MarcSubfieldStructures.t b/t/db_dependent/Koha/MarcSubfieldStructures.t
index d65f4cc633..7a755d9851 100644
--- a/t/db_dependent/Koha/MarcSubfieldStructures.t
+++ b/t/db_dependent/Koha/MarcSubfieldStructures.t
@@ -21,7 +21,6 @@ use Modern::Perl;
 
 use Test::More tests => 1;
 
-use Koha::MarcSubfieldStructure;
 use Koha::MarcSubfieldStructures;
 use Koha::Database;