diff --git a/doc/ZeroCopyRx.c b/doc/ZeroCopyRx.c
index c5191326..e8bda20f 100644
--- a/doc/ZeroCopyRx.c
+++ b/doc/ZeroCopyRx.c
@@ -12,6 +12,9 @@ void my_pbuf_free_custom(void* p)
 
   my_custom_pbuf_t* my_puf = (my_custom_pbuf_t*)p;
 
+  // flush data cache here - lwIP and/or application may have written into buffer!
+  flush_cpu_cache(p->payload, p->tot_len);
+
   SYS_ARCH_PROTECT(old_level);
   free_rx_dma_descriptor(my_pbuf->dma_descriptor);
   LWIP_MEMPOOL_FREE(RX_POOL, my_pbuf);