diff --git a/services/loopback/common/methods/sale/updateQuantity.js b/services/loopback/common/methods/sale/updateQuantity.js
new file mode 100644
index 0000000000..eac9ac3090
--- /dev/null
+++ b/services/loopback/common/methods/sale/updateQuantity.js
@@ -0,0 +1,34 @@
+module.exports = Self => {
+    Self.remoteMethod('updateQuantity', {
+        description: 'Changes the quantity of a sale',
+        accessType: '',
+        accepts: [{
+            arg: 'id',
+            type: 'number',
+            required: true,
+            description: 'sale ID',
+            http: {source: 'path'}
+        }, {
+            arg: 'quantity',
+            type: 'number',
+            required: true,
+            description: 'newQuantity'
+        }],
+        returns: {
+            type: 'string',
+            root: true
+        },
+        http: {
+            path: `/:id/updateQuantity`,
+            verb: 'post'
+        }
+    });
+
+    Self.updateQuantity = async(id, quantity) => {
+        let currentLine = await Self.app.models.Sale.findOne({where: {id: id}, fields: ['quantity']});
+        if (quantity > currentLine.quantity)
+            throw new Error('The new quantity should be smaller than the old one');
+
+        return await Self.app.models.Sale.update({id: id}, {quantity: quantity});
+    };
+};