diff --git a/src/core/ipv4/etharp.c b/src/core/ipv4/etharp.c
index efafcea2..d76b7f2b 100644
--- a/src/core/ipv4/etharp.c
+++ b/src/core/ipv4/etharp.c
@@ -996,13 +996,12 @@ etharp_query(struct netif *netif, const ip4_addr_t *ipaddr, struct pbuf *q)
     /* entry is still pending, queue the given packet 'q' */
     struct pbuf *p;
     int copy_needed = 0;
-    /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
-     * to copy the whole queue into a new PBUF_RAM (see bug #11400)
-     * PBUF_ROMs can be left as they are, since ROM must not get changed. */
+    /* IF q includes a pbuf that must be copied, copy the whole chain into a
+     * new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
     p = q;
     while (p) {
       LWIP_ASSERT("no packet queues allowed!", (p->len != p->tot_len) || (p->next == 0));
-      if (p->type != PBUF_ROM) {
+      if (PBUF_NEEDS_COPY(p)) {
         copy_needed = 1;
         break;
       }
diff --git a/src/core/ipv6/nd6.c b/src/core/ipv6/nd6.c
index df57df12..18b6b755 100644
--- a/src/core/ipv6/nd6.c
+++ b/src/core/ipv6/nd6.c
@@ -2034,12 +2034,11 @@ nd6_queue_packet(s8_t neighbor_index, struct pbuf *q)
     return ERR_ARG;
   }
 
-  /* IF q includes a PBUF_REF, PBUF_POOL or PBUF_RAM, we have no choice but
-   * to copy the whole queue into a new PBUF_RAM (see bug #11400)
-   * PBUF_ROMs can be left as they are, since ROM must not get changed. */
+  /* IF q includes a pbuf that must be copied, we have to copy the whole chain
+   * into a new PBUF_RAM. See the definition of PBUF_NEEDS_COPY for details. */
   p = q;
   while (p) {
-    if (p->type != PBUF_ROM) {
+    if (PBUF_NEEDS_COPY(p)) {
       copy_needed = 1;
       break;
     }
diff --git a/src/include/lwip/pbuf.h b/src/include/lwip/pbuf.h
index 3ce8449d..c2238028 100644
--- a/src/include/lwip/pbuf.h
+++ b/src/include/lwip/pbuf.h
@@ -55,6 +55,22 @@ extern "C" {
 #define LWIP_SUPPORT_CUSTOM_PBUF ((IP_FRAG && !LWIP_NETIF_TX_SINGLE_PBUF) || (LWIP_IPV6 && LWIP_IPV6_FRAG))
 #endif
 
+/** PBUF_NEEDS_COPY(p): return a boolean value indicating whether the given
+ * pbuf needs to be copied in order to be kept around beyond the current call
+ * stack without risking being corrupted. The default setting provides safety:
+ * it will make a copy iof any pbuf chain that does not consist entirely of
+ * PBUF_ROM type pbufs. For setups with zero-copy support, it may be redefined
+ * to evaluate to true in all cases, for example. However, doing so also has an
+ * effect on the application side: any buffers that are *not* copied must also
+ * *not* be reused by the application after passing them to lwIP. For example,
+ * when setting PBUF_NEEDS_COPY to (0), after using udp_send() with a PBUF_RAM
+ * pbuf, the application must free the pbuf immediately, rather than reusing it
+ * for other purposes. For more background information on this, see tasks #6735
+ * and #7896, and bugs #11400 and #49914. */
+#ifndef PBUF_NEEDS_COPY
+#define PBUF_NEEDS_COPY(p)  ((p)->type != PBUF_ROM)
+#endif /* PBUF_NEEDS_COPY */
+
 /* @todo: We need a mechanism to prevent wasting memory in every pbuf
    (TCP vs. UDP, IPv4 vs. IPv6: UDP/IPv4 packets may waste up to 28 bytes) */