diff --git a/src/Model/Scope.php b/src/Model/Scope.php
index a3db0a4fa2..3a13f751b3 100644
--- a/src/Model/Scope.php
+++ b/src/Model/Scope.php
@@ -89,7 +89,7 @@ public function addCondition($field, $operator = null, $value = null)
         return $this;
     }
 
-    protected function setSystem($system = true)
+    protected function setSystem(bool $system = true)
     {
         foreach ($this->elements as $nestedCondition) {
             $nestedCondition->setSystem($system && $this->isAnd());
diff --git a/src/Model/Scope/AbstractScope.php b/src/Model/Scope/AbstractScope.php
index badfa0f7c5..2257e2ce50 100644
--- a/src/Model/Scope/AbstractScope.php
+++ b/src/Model/Scope/AbstractScope.php
@@ -34,14 +34,17 @@ protected function init(): void
         $this->_init();
 
         // always set system flag if condition added to another condition
-        $this->setSystem($this->owner instanceof RootScope);
+        $this->setSystem($owner instanceof RootScope);
 
         $this->onChangeModel();
     }
 
     abstract protected function onChangeModel(): void;
 
-    abstract protected function setSystem($system = true);
+    /**
+     * @return $this
+     */
+    abstract protected function setSystem(bool $system = true);
 
     /**
      * Get the model this condition is associated with.
diff --git a/src/Model/Scope/Condition.php b/src/Model/Scope/Condition.php
index 2c1a563254..8be81e6c00 100644
--- a/src/Model/Scope/Condition.php
+++ b/src/Model/Scope/Condition.php
@@ -151,7 +151,7 @@ public function __construct($key, $operator = null, $value = null)
         }
     }
 
-    protected function setSystem($system = true)
+    protected function setSystem(bool $system = true)
     {
         $this->system = $system;