diff --git a/tests/aws/requests/rds/helper.rb b/tests/aws/requests/rds/helper.rb
index 63ec0193f..75e1b8447 100644
--- a/tests/aws/requests/rds/helper.rb
+++ b/tests/aws/requests/rds/helper.rb
@@ -115,6 +115,7 @@ class AWS
             'Status' => String,
             'DBSecurityGroupName' => String
           }],
+        'DBSubnetGroupName' => Fog::Nullable::String,
         'Endpoint' => {
           'Address' => Fog::Nullable::String,
           'Port' => Fog::Nullable::Integer