diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9cc9e57ec..01c07c64d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changelog Fab-manager
 
 - Fix a bug: unable to show calendar for Firefox and Safari
+- Improved error message for event reservation
 
 ## v6.0.4 2023 April 25
 
diff --git a/app/frontend/src/javascript/controllers/events.js.erb b/app/frontend/src/javascript/controllers/events.js.erb
index 8fe4e618a..09b5ab08c 100644
--- a/app/frontend/src/javascript/controllers/events.js.erb
+++ b/app/frontend/src/javascript/controllers/events.js.erb
@@ -372,7 +372,7 @@ Application.Controllers.controller('ShowEventController', ['$scope', '$state', '
       }
       , function (response) {
       // reservation failed
-        growl.error(response && response.data && response.data.card && response.data.card[0] || 'server error');
+        growl.error(response && response.data && _.keys(response.data)[0] && response.data[_.keys(response.data)[0]][0] || 'server error');
         // unset the attempting marker
         $scope.attempting = false;
       })