diff --git a/library/Vspheredb/Web/Form/PerfdataConsumerForm.php b/library/Vspheredb/Web/Form/PerfdataConsumerForm.php
index 06c18679..0fbca0d3 100644
--- a/library/Vspheredb/Web/Form/PerfdataConsumerForm.php
+++ b/library/Vspheredb/Web/Form/PerfdataConsumerForm.php
@@ -56,7 +56,7 @@ public function assemble()
         $this->addButtons(isset($implementation), 'implementation');
     }
 
-    public function isValidEvent($event)
+    public function isValidEvent($event): bool
     {
         if ($event === self::ON_DELETE) {
             return true;
diff --git a/library/Vspheredb/Web/Form/VCenterShipMetricsForm.php b/library/Vspheredb/Web/Form/VCenterShipMetricsForm.php
index a4a7f8c7..042f7ad3 100644
--- a/library/Vspheredb/Web/Form/VCenterShipMetricsForm.php
+++ b/library/Vspheredb/Web/Form/VCenterShipMetricsForm.php
@@ -121,7 +121,7 @@ protected function addConsumerConfig($consumer)
         }
     }
 
-    public function isValidEvent($event)
+    public function isValidEvent($event): bool
     {
         if ($event === self::ON_DELETE) {
             return true;