diff --git a/lib/stripe_mock/database.ex b/lib/stripe_mock/database.ex
index aa51357..216b31d 100644
--- a/lib/stripe_mock/database.ex
+++ b/lib/stripe_mock/database.ex
@@ -26,7 +26,8 @@ defmodule StripeMock.Database do
       database: database,
       hostname: host,
       port: port,
-      pool_size: 2
+      pool_size: 2,
+      migration_primary_key: [type: :string]
     ]
 
     {:ok, config}