diff --git a/src/Bundle/ChillMainBundle/Export/ExportManager.php b/src/Bundle/ChillMainBundle/Export/ExportManager.php
index f8ff95fe1..9a26f70ad 100644
--- a/src/Bundle/ChillMainBundle/Export/ExportManager.php
+++ b/src/Bundle/ChillMainBundle/Export/ExportManager.php
@@ -148,7 +148,7 @@ class ExportManager
      *
      * @throws \RuntimeException if the aggregator is not known
      */
-    public function getAggregator($alias)
+    public function getAggregator($alias): AggregatorInterface
     {
         if (null === $aggregator = $this->aggregators[$alias] ?? null) {
             throw new \RuntimeException("The aggregator with alias {$alias} is not known.");