diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 750d7361..37517005 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -481,6 +481,7 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
     LWIP_ASSERT("inconsistent oversize vs. len", (oversize == 0) || (pos == len));
 #endif /* TCP_OVERSIZE */
 
+#if !LWIP_NETIF_TX_SINGLE_PBUF
     /*
      * Phase 2: Chain a new pbuf to the end of pcb->unsent.
      *
@@ -491,6 +492,10 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
      * We don't extend segments containing SYN/FIN flags or options
      * (len==0). The new pbuf is kept in concat_p and pbuf_cat'ed at
      * the end.
+     *
+     * This phase is skipped for LWIP_NETIF_TX_SINGLE_PBUF as we could only execute
+     * it after rexmit puts a segment from unacked to unsent and at this point,
+     * oversize info is lost.
      */
     if ((pos < len) && (space > 0) && (last_unsent->len > 0)) {
       u16_t seglen = LWIP_MIN(space, len - pos);
@@ -549,6 +554,7 @@ tcp_write(struct tcp_pcb *pcb, const void *arg, u16_t len, u8_t apiflags)
                 pcb->unsent_oversize == 0);
 #endif /* TCP_OVERSIZE */
   }
+#endif /* !LWIP_NETIF_TX_SINGLE_PBUF */
 
   /*
    * Phase 3: Create new segments.