https://savannah.nongnu.org/patch/index.php?10410

diff --git a/src/core/ipv6/ip6_addr.c b/src/core/ipv6/ip6_addr.c
index aafba72..3964d71 100644
--- a/src/core/ipv6/ip6_addr.c
+++ b/src/core/ipv6/ip6_addr.c
@@ -266,7 +266,7 @@ ip6addr_ntoa_r(const ip6_addr_t *addr, char *buf, int buflen)
         }
         break;
       }
-      if (empty_block_flag == 0) {
+      if (empty_block_flag == 0 && current_block_index < 7) {
         /* generate empty block "::", but only if more than one contiguous zero block,
          * according to current formatting suggestions RFC 5952. */
         next_block_value = lwip_htonl(addr->addr[(current_block_index + 1) >> 1]);
