diff --git a/src/core/ipv6/ip6_frag.c b/src/core/ipv6/ip6_frag.c
index e47cf9df..50d73473 100644
--- a/src/core/ipv6/ip6_frag.c
+++ b/src/core/ipv6/ip6_frag.c
@@ -559,12 +559,13 @@ ip6_reass(struct pbuf *p)
 
 #if IPV6_FRAG_COPYHEADER
     if (IPV6_FRAG_REQROOM > 0) {
+      u8_t hdrerr;
       /* Restore (only) the bytes that we overwrote beyond the fragment header.
        * Those bytes may belong to either the IPv6 header or an extension
        * header placed before the fragment header. */
       MEMCPY(p->payload, ipr->orig_hdr, IPV6_FRAG_REQROOM);
       /* get back room for struct ip6_reass_helper (only required if sizeof(void*) > 4) */
-      u8_t hdrerr = pbuf_header(p, -(s16_t)(IPV6_FRAG_REQROOM));
+      hdrerr = pbuf_header(p, -(s16_t)(IPV6_FRAG_REQROOM));
       LWIP_UNUSED_ARG(hdrerr); /* in case of LWIP_NOASSERT */
       LWIP_ASSERT("no room for struct ip6_reass_helper", hdrerr == 0);
     }