diff --git a/examples/relationships.php b/examples/relationships.php
index bf14fd6..d161cd8 100644
--- a/examples/relationships.php
+++ b/examples/relationships.php
@@ -82,6 +82,14 @@
 $jsonapi->add_relation('one-by-one-neighbours', $ship1_resource, $skip_include=false, $type=jsonapi\resource::RELATION_TO_MANY);
 $jsonapi->add_relation('one-by-one-neighbours', $dock_resource, $skip_include=false, $type=jsonapi\resource::RELATION_TO_MANY);
 
+/**
+ * custom
+ */
+$custom_relation = [
+	'data' => ['cus' => 'tom'],
+];
+$jsonapi->add_relation('custom', $custom_relation);
+
 /**
  * sending the response
  */
diff --git a/src/resource.php b/src/resource.php
index 7477ac0..853c539 100644
--- a/src/resource.php
+++ b/src/resource.php
@@ -269,8 +269,10 @@ public function add_relation($key, $relation, $skip_include=false, $type=null) {
 	
 	if (is_array($relation)) {
 		$this->primary_relationships[$key] = $relation;
+		return;
 	}
-	elseif ($relation instanceof \alsvanzelf\jsonapi\resource) {
+	
+	if ($relation instanceof \alsvanzelf\jsonapi\resource) {
 		// add whole resources as included resource, while keeping the relationship
 		if ($relation->has_data() && $skip_include == false) {
 			$this->add_included_resource($relation);