diff --git a/CHANGELOG.md b/CHANGELOG.md
index 985870c22..7bb47391e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changelog Fab Manager
 
 - Fix a bug: no user can be created after the last member was deleted
+- Fix a bug: unable to generate a refund (Avoir)
 - Fix a security issue: updated lodash to 4.17.14 to fix [CVE-2019-10744](https://github.com/lodash/lodash/pull/4336)
 - Fix a security issue: updated mini_magick to 4.9.4 to fix [CVE-2019-13574](https://nvd.nist.gov/vuln/detail/CVE-2019-13574)
 - Fix some security issues: updated bootstrap to 3.4.1 to fix [CVE-2019-8331](https://nvd.nist.gov/vuln/detail/CVE-2019-8331), [CVE-2019-14041](https://nvd.nist.gov/vuln/detail/CVE-2018-14041), and 3 other low severity CVE
diff --git a/app/assets/javascripts/controllers/admin/invoices.js.erb b/app/assets/javascripts/controllers/admin/invoices.js.erb
index 6e87bc394..3115f50f2 100644
--- a/app/assets/javascripts/controllers/admin/invoices.js.erb
+++ b/app/assets/javascripts/controllers/admin/invoices.js.erb
@@ -619,8 +619,12 @@ Application.Controllers.controller('AvoirModalController', ['$scope', '$uibModal
       // check that at least 1 element of the invoice is refunded
       $scope.avoir.invoice_items_ids = [];
       for (let itemId in $scope.partial) {
-        const refundItem = $scope.partial[itemId];
-        if (refundItem) { $scope.avoir.invoice_items_ids.push(parseInt(itemId)); }
+        if (Object.prototype.hasOwnProperty.call($scope.partial, itemId)) {
+          const refundItem = $scope.partial[itemId];
+          if (refundItem) {
+            $scope.avoir.invoice_items_ids.push(parseInt(itemId));
+          }
+        }
       }
 
       if ($scope.avoir.invoice_items_ids.length === 0) {
diff --git a/app/services/invoices_service.rb b/app/services/invoices_service.rb
index 3a0f45e0c..127cd5359 100644
--- a/app/services/invoices_service.rb
+++ b/app/services/invoices_service.rb
@@ -10,7 +10,7 @@ class InvoicesService
   # @param filters {Hash} allowed filters: number, customer, date.
   def self.list(order_key, direction, page, size, filters = {})
     invoices = Invoice.includes(:avoir, :invoicing_profile, invoice_items: %i[subscription invoice_item])
-                      .joins(:invoicing_profile)
+                      .joins('invoicing_profile')
                       .order("#{order_key} #{direction}")
                       .page(page)
                       .per(size)
diff --git a/app/views/api/invoices/show.json.jbuilder b/app/views/api/invoices/show.json.jbuilder
index 041d2e510..d4087a0b8 100644
--- a/app/views/api/invoices/show.json.jbuilder
+++ b/app/views/api/invoices/show.json.jbuilder
@@ -1,4 +1,7 @@
-json.extract! @invoice, :id, :created_at, :reference, :invoiced_type, :user_id, :avoir_date, :description
+# frozen_string_literal: true
+
+json.extract! @invoice, :id, :created_at, :reference, :invoiced_type, :avoir_date, :description
+json.user_id @invoice.invoicing_profile&.user_id
 json.total (@invoice.total / 100.00)
 json.name @invoice.user.profile.full_name
 json.has_avoir @invoice.refunded?