diff --git a/lib/HttpRequestGraphQL.php b/lib/HttpRequestGraphQL.php
index 10d902f..fe6106c 100644
--- a/lib/HttpRequestGraphQL.php
+++ b/lib/HttpRequestGraphQL.php
@@ -49,6 +49,8 @@ protected static function prepareRequest($httpHeaders = array(), $data = array()
 
         if (is_array($variables)) {
             self::$postDataGraphQL = json_encode(['query' => $data, 'variables' => $variables]);
+        } else {
+            self::$postDataGraphQL = json_encode(['query' => $data]);
         }
     }