diff --git a/extmod/modlwip.c b/extmod/modlwip.c
index ced9c06a1b..0f3ab7c155 100644
--- a/extmod/modlwip.c
+++ b/extmod/modlwip.c
@@ -184,7 +184,7 @@ typedef struct _lwip_socket_obj_t {
     mp_obj_base_t base;
 
     void *pcb;
-    void *incoming;
+    void *volatile incoming;
     byte peer[4];
     mp_uint_t peer_port;
     mp_uint_t timeout;