diff --git a/library/Icingadb/Model/Schema.php b/library/Icingadb/Model/Schema.php
index 10320a315..4d7618ffc 100644
--- a/library/Icingadb/Model/Schema.php
+++ b/library/Icingadb/Model/Schema.php
@@ -19,17 +19,17 @@
  */
 class Schema extends Model
 {
-    public function getTableName()
+    public function getTableName(): string
     {
         return 'icingadb_schema';
     }
 
-    public function getKeyName()
+    public function getKeyName(): string
     {
         return 'id';
     }
 
-    public function getColumns()
+    public function getColumns(): array
     {
         return [
             'version',
@@ -37,12 +37,12 @@ public function getColumns()
         ];
     }
 
-    public function getDefaultSort()
+    public function getDefaultSort(): array
     {
         return ['timestamp desc'];
     }
 
-    public function createBehaviors(Behaviors $behaviors)
+    public function createBehaviors(Behaviors $behaviors): void
     {
         $behaviors->add(new Binary(['id']));
         $behaviors->add(new MillisecondTimestamp(['timestamp']));