diff --git a/src/Api/MailingList/Member.php b/src/Api/MailingList/Member.php
index 6d9775e..4995a9f 100644
--- a/src/Api/MailingList/Member.php
+++ b/src/Api/MailingList/Member.php
@@ -152,6 +152,7 @@ class Member extends HttpApi
                     case 'vars':
                         if (is_array($value)) {
                             $value = json_encode($value);
+                            $parameters[$field] = $value;
                         }
                         // We should assert that "vars"'s $value is a string.
                         // no break
@@ -199,6 +200,7 @@ class Member extends HttpApi
                 case 'vars':
                     if (is_array($value)) {
                         $value = json_encode($value);
+                        $parameters[$field] = $value;
                     }
                     // We should assert that "vars"'s $value is a string.
                     // no break