diff --git a/src/core/ipv6/icmp6.c b/src/core/ipv6/icmp6.c
index 167738a0..f2369716 100644
--- a/src/core/ipv6/icmp6.c
+++ b/src/core/ipv6/icmp6.c
@@ -57,9 +57,9 @@
 
 #include <string.h>
 
-#if LWIP_ICMP6_DATASIZE == 0
+#if !LWIP_ICMP6_DATASIZE || (LWIP_ICMP6_DATASIZE > (IP6_MIN_MTU_LENGTH - IP6_HLEN - ICMP6_HLEN))
 #undef LWIP_ICMP6_DATASIZE
-#define LWIP_ICMP6_DATASIZE   8
+#define LWIP_ICMP6_DATASIZE   (IP6_MIN_MTU_LENGTH - IP6_HLEN - ICMP6_HLEN)
 #endif
 
 /* Forward declarations */
@@ -387,17 +387,18 @@ icmp6_send_response_with_addrs_and_netif(struct pbuf *p, u8_t code, u32_t data,
 {
   struct pbuf *q;
   struct icmp6_hdr *icmp6hdr;
+  u16_t datalen = LWIP_MIN(p->tot_len, LWIP_ICMP6_DATASIZE);
 
-  /* ICMPv6 header + IPv6 header + data */
-  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp6_hdr) + IP6_HLEN + LWIP_ICMP6_DATASIZE,
+  /* ICMPv6 header + datalen (as much of the offending packet as possible) */
+  q = pbuf_alloc(PBUF_IP, sizeof(struct icmp6_hdr) + datalen,
                  PBUF_RAM);
   if (q == NULL) {
     LWIP_DEBUGF(ICMP_DEBUG, ("icmp_time_exceeded: failed to allocate pbuf for ICMPv6 packet.\n"));
     ICMP6_STATS_INC(icmp6.memerr);
     return;
   }
-  LWIP_ASSERT("check that first pbuf can hold icmp 6message",
-             (q->len >= (sizeof(struct icmp6_hdr) + IP6_HLEN + LWIP_ICMP6_DATASIZE)));
+  LWIP_ASSERT("check that first pbuf can hold icmp6 header",
+             (q->len >= (sizeof(struct icmp6_hdr))));
 
   icmp6hdr = (struct icmp6_hdr *)q->payload;
   icmp6hdr->type = type;
@@ -405,8 +406,7 @@ icmp6_send_response_with_addrs_and_netif(struct pbuf *p, u8_t code, u32_t data,
   icmp6hdr->data = lwip_htonl(data);
 
   /* copy fields from original packet */
-  SMEMCPY((u8_t *)q->payload + sizeof(struct icmp6_hdr), (u8_t *)p->payload,
-          IP6_HLEN + LWIP_ICMP6_DATASIZE);
+  pbuf_take_at(q, p->payload, datalen, sizeof(struct icmp6_hdr));
 
   /* calculate checksum */
   icmp6hdr->chksum = 0;
diff --git a/src/include/lwip/opt.h b/src/include/lwip/opt.h
index 8dcf0aa5..d8c82d15 100644
--- a/src/include/lwip/opt.h
+++ b/src/include/lwip/opt.h
@@ -2496,10 +2496,12 @@
 
 /**
  * LWIP_ICMP6_DATASIZE: bytes from original packet to send back in
- * ICMPv6 error messages.
+ * ICMPv6 error messages (0 = default of IP6_MIN_MTU_LENGTH)
+ * ATTENTION: RFC4443 section 2.4 says IP6_MIN_MTU_LENGTH is a MUST,
+ * so override this only if you absolutely have to!
  */
 #if !defined LWIP_ICMP6_DATASIZE || defined __DOXYGEN__
-#define LWIP_ICMP6_DATASIZE             8
+#define LWIP_ICMP6_DATASIZE             0
 #endif
 
 /**
diff --git a/src/include/lwip/prot/icmp6.h b/src/include/lwip/prot/icmp6.h
index 34611204..36989f6b 100644
--- a/src/include/lwip/prot/icmp6.h
+++ b/src/include/lwip/prot/icmp6.h
@@ -146,6 +146,8 @@ PACK_STRUCT_END
 #  include "arch/epstruct.h"
 #endif
 
+#define ICMP6_HLEN 8
+
 /** This is the ICMP6 header adapted for echo req/resp. */
 #ifdef PACK_STRUCT_USE_INCLUDES
 #  include "arch/bpstruct.h"