diff --git a/src/Bundle/ChillActivityBundle/Export/Aggregator/ACPAggregators/ByActivityNumberAggregator.php b/src/Bundle/ChillActivityBundle/Export/Aggregator/ACPAggregators/ByActivityNumberAggregator.php
index de35f75cc..5c6656009 100644
--- a/src/Bundle/ChillActivityBundle/Export/Aggregator/ACPAggregators/ByActivityNumberAggregator.php
+++ b/src/Bundle/ChillActivityBundle/Export/Aggregator/ACPAggregators/ByActivityNumberAggregator.php
@@ -11,6 +11,7 @@ declare(strict_types=1);
 
 namespace Chill\ActivityBundle\Export\Aggregator\ACPAggregators;
 
+use Chill\ActivityBundle\Entity\Activity;
 use Chill\MainBundle\Export\AggregatorInterface;
 use Chill\PersonBundle\Export\Declarations;
 use Doctrine\ORM\QueryBuilder;
@@ -23,9 +24,10 @@ class ByActivityNumberAggregator implements AggregatorInterface
         return null;
     }
 
-    public function alterQuery(QueryBuilder $qb, $data)
+    public function alterQuery(QueryBuilder $qb, $data): void
     {
-        $qb->addSelect('AS activity_by_number_aggregator')
+        $qb
+            ->addSelect('(SELECT COUNT(activity.id) FROM ' . Activity::class . ' activity WHERE activity.accompanyingPeriod = acp) AS activity_by_number_aggregator')
             ->addGroupBy('activity_by_number_aggregator');
     }
 
@@ -34,17 +36,23 @@ class ByActivityNumberAggregator implements AggregatorInterface
         return Declarations::ACP_TYPE;
     }
 
-    public function buildForm(FormBuilderInterface $builder)
+    public function buildForm(FormBuilderInterface $builder): void
     {
         // No form needed
     }
 
     public function getLabels($key, array $values, $data)
     {
-        return static function ($value): string {
+        return static function ($value) {
             if ('_header' === $value) {
                 return '';
             }
+
+            if (null === $value) {
+                return '';
+            }
+
+            return $value;
         };
     }