diff --git a/packages/authentication-oauth/src/index.ts b/packages/authentication-oauth/src/index.ts
index 3474f7ed33..de15449b40 100644
--- a/packages/authentication-oauth/src/index.ts
+++ b/packages/authentication-oauth/src/index.ts
@@ -30,7 +30,6 @@ export const setup = (options: OauthSetupSettings) => (app: Application) => {
   const { strategyNames } = service
 
   // Set up all the defaults
-  const { prefix = '/oauth' } = oauth.defaults || {}
   const port = app.get('port')
   let host = app.get('host')
   let protocol = 'https'
@@ -44,20 +43,21 @@ export const setup = (options: OauthSetupSettings) => (app: Application) => {
   }
 
   const grant = defaultsDeep(
+    {},
+    omit(oauth, ['redirect', 'origins']),
     {
       defaults: {
-        prefix,
-        origin: `${oauth?.defaults?.protocol ?? protocol}://${oauth?.defaults?.host ?? host}`,
-        transport: oauth?.defaults?.transport ?? 'session',
+        prefix: '/oauth',
+        origin: `${protocol}://${host}`,
+        transport: 'session',
         response: ['tokens', 'raw', 'profile']
       }
-    },
-    omit(oauth, ['redirect', 'origins'])
+    }
   )
 
   const getUrl = (url: string) => {
     const { defaults } = grant
-    return `${defaults.origin}${prefix}/${url}`
+    return `${defaults.origin}${defaults.prefix}/${url}`
   }
 
   each(grant, (value, name) => {