diff --git a/src/core/Form/Type/CollectionType.php b/src/core/Form/Type/CollectionType.php
index 166d5d5..c4f6e1e 100644
--- a/src/core/Form/Type/CollectionType.php
+++ b/src/core/Form/Type/CollectionType.php
@@ -34,7 +34,7 @@ class CollectionType extends BaseCollectionType
         ]);
     }
 
-    public function getBlockPrefix()
+    public function getBlockPrefix(): string
     {
         return 'murph_collection';
     }