diff --git a/db/dump/fixtures.before.sql b/db/dump/fixtures.before.sql
index 6563292dd..5e6533b28 100644
--- a/db/dump/fixtures.before.sql
+++ b/db/dump/fixtures.before.sql
@@ -632,7 +632,7 @@ INSERT INTO `vn`.`invoiceOutSerial` (`code`, `description`, `isTaxed`, `taxAreaF
         ('A', 'Global nacional',            1, 'NATIONAL',  0,  'global'),
         ('T', 'Española rapida',            1, 'NATIONAL',  0,  'quick'),
         ('V', 'Intracomunitaria global',    0, 'CEE',       1,  'global'),
-        ('M', 'Múltiple nacional',          1, 'NATIONAL',  0,  'quick'),
+        ('M', 'Múltiple nacional',          1, 'NATIONAL',  0,  'multiple'),
         ('R', 'Rectificativa',              1, 'NATIONAL',  0,   NULL),
         ('E', 'Exportación rápida',         0, 'WORLD',     0,  'quick');
 
diff --git a/db/routines/vn/functions/invoiceSerial.sql b/db/routines/vn/functions/invoiceSerial.sql
index 5ce20dc8b..0269275b1 100644
--- a/db/routines/vn/functions/invoiceSerial.sql
+++ b/db/routines/vn/functions/invoiceSerial.sql
@@ -12,7 +12,7 @@ BEGIN
 	* @param vType Tipo de factura ['global','multiple','quick']
 	* @return vSerie de la factura
 	*/
-	DECLARE vTaxArea VARCHAR(25);
+	DECLARE vTaxArea VARCHAR(25) COLLATE utf8mb3_general_ci;
 	DECLARE vSerie CHAR(2);
 
 	IF (SELECT hasInvoiceSimplified FROM client WHERE id = vClientFk) THEN
diff --git a/db/versions/11142-aquaGerbera/00-invoiceOutSerialColumn.sql b/db/versions/11142-aquaGerbera/00-invoiceOutSerialColumn.sql
index db476c4a5..09ac00401 100644
--- a/db/versions/11142-aquaGerbera/00-invoiceOutSerialColumn.sql
+++ b/db/versions/11142-aquaGerbera/00-invoiceOutSerialColumn.sql
@@ -1,2 +1,4 @@
 ALTER TABLE vn.invoiceOutSerial
 	MODIFY COLUMN `type` enum('global','quick','multiple') CHARACTER SET utf8mb3 COLLATE utf8mb3_unicode_ci DEFAULT NULL NULL;
+
+CREATE UNIQUE INDEX invoiceOutSerial_taxAreaFk_IDX USING BTREE ON vn.invoiceOutSerial (taxAreaFk,`type`);
diff --git a/db/versions/11142-aquaGerbera/01-invoiceOutSerialUpdate.sql b/db/versions/11142-aquaGerbera/01-invoiceOutSerialUpdate.sql
index 581a6f5f3..fad33b5dc 100644
--- a/db/versions/11142-aquaGerbera/01-invoiceOutSerialUpdate.sql
+++ b/db/versions/11142-aquaGerbera/01-invoiceOutSerialUpdate.sql
@@ -1,3 +1,3 @@
 UPDATE vn.invoiceOutSerial
 	SET `type`='multiple'
-	WHERE `description` LIKE '%multiple%';
+	WHERE `description` LIKE '%Múltiple%';
diff --git a/modules/invoiceIn/back/methods/invoice-in/getSerial.js b/modules/invoiceIn/back/methods/invoice-in/getSerial.js
index dcc1fbc3c..29c7cae2f 100644
--- a/modules/invoiceIn/back/methods/invoice-in/getSerial.js
+++ b/modules/invoiceIn/back/methods/invoice-in/getSerial.js
@@ -46,7 +46,7 @@ module.exports = Self => {
             }
         });
 
-        filter = mergeFilters(args.filter, {where});
+        const filter = mergeFilters(args.filter, {where});
 
         const stmt = new ParameterizedSQL(
             `SELECT i.serial, SUM(IF(i.isBooked, 0,1)) pending, COUNT(*) total