diff --git a/sys/net/network_layer/ng_ipv6/ext/ng_ipv6_ext.c b/sys/net/network_layer/ng_ipv6/ext/ng_ipv6_ext.c
index 8919291e0f..1f746e0ad0 100644
--- a/sys/net/network_layer/ng_ipv6/ext/ng_ipv6_ext.c
+++ b/sys/net/network_layer/ng_ipv6/ext/ng_ipv6_ext.c
@@ -71,6 +71,10 @@ ng_pktsnip_t *ng_ipv6_ext_build(ng_pktsnip_t *ipv6, ng_pktsnip_t *next,
     ng_pktsnip_t *prev = NULL, *snip;
     ng_ipv6_ext_t *ext;
 
+    if (size < NG_IPV6_EXT_LEN_UNIT) {
+        return NULL;
+    }
+
     if (ipv6 != NULL) {
         LL_SEARCH_SCALAR(ipv6, prev, next, next);
 
@@ -79,10 +83,6 @@ ng_pktsnip_t *ng_ipv6_ext_build(ng_pktsnip_t *ipv6, ng_pktsnip_t *next,
         }
     }
 
-    if (size < NG_IPV6_EXT_LEN_UNIT) {
-        return NULL;
-    }
-
     snip = ng_pktbuf_add(next, NULL, size, NG_NETTYPE_IPV6);
 
     if (snip == NULL) {