diff --git a/standalone.js b/standalone.js
index 7f0d40a..e593fb1 100644
--- a/standalone.js
+++ b/standalone.js
@@ -11,7 +11,7 @@ function SerializerSelector () {
 
 function responseSchemaCompiler (fjsOpts, { schema /* method, url, httpStatus */ }) {
   if (fjsOpts.schema && schema.$id && fjsOpts.schema[schema.$id]) {
-    fjsOpts.schema = { ...fjsOpts.schema }
+    fjsOpts = { ...fjsOpts, schema: { ...fjsOpts.schema } }
     delete fjsOpts.schema[schema.$id]
   }
   return fastJsonStringify(schema, fjsOpts)
diff --git a/test/duplicate-schema.test.js b/test/duplicate-schema.test.js
index 2acaa24..e1e4377 100644
--- a/test/duplicate-schema.test.js
+++ b/test/duplicate-schema.test.js
@@ -24,3 +24,22 @@ test('Use input schema duplicate in the externalSchemas', async t => {
 
   t.assert.ok(true)
 })
+
+test('Keep the external schemas for later compilations', async t => {
+  t.plan(1)
+  const externalSchemas = {
+    schema1: {
+      $id: 'schema1',
+      type: 'object',
+      properties: { name: { type: 'string' } }
+    }
+  }
+
+  const factory = FjsCompiler()
+  const compiler = factory(externalSchemas)
+
+  compiler({ schema: externalSchemas.schema1 })
+  const serialize = compiler({ schema: { $ref: 'schema1#' } })
+
+  t.assert.equal(serialize({ name: 'a', secret: 1 }), '{"name":"a"}')
+})