diff --git a/packages/start-client-core/src/client/hydrateStart.ts b/packages/start-client-core/src/client/hydrateStart.ts
index 6f51ca03f68..e807d7ec153 100644
--- a/packages/start-client-core/src/client/hydrateStart.ts
+++ b/packages/start-client-core/src/client/hydrateStart.ts
@@ -25,6 +25,9 @@ export async function hydrateStart(): Promise<AnyRouter> {
   }
 
   serializationAdapters.push(ServerFunctionSerializationAdapter)
+  if (router.options.serializationAdapters) {
+    serializationAdapters.push(...router.options.serializationAdapters)
+  }
 
   router.update({
     basepath: process.env.TSS_ROUTER_BASEPATH,
diff --git a/packages/start-server-core/src/createStartHandler.ts b/packages/start-server-core/src/createStartHandler.ts
index 48a180ea123..1589a04dc1a 100644
--- a/packages/start-server-core/src/createStartHandler.ts
+++ b/packages/start-server-core/src/createStartHandler.ts
@@ -145,7 +145,10 @@ export function createStartHandler<TRegister = Register>(
         origin: router.options.origin ?? origin,
         ...{
           defaultSsr: startOptions.defaultSsr,
-          serializationAdapters: startOptions.serializationAdapters,
+          serializationAdapters: [
+            ...(startOptions.serializationAdapters || []),
+            ...(router.options.serializationAdapters || []),
+          ],
         },
         basepath: ROUTER_BASEPATH,
       })