diff --git a/src/netif/lowpan6.c b/src/netif/lowpan6.c
index 582d8b8e..15d10278 100644
--- a/src/netif/lowpan6.c
+++ b/src/netif/lowpan6.c
@@ -564,7 +564,7 @@ lowpan6_frag(struct netif *netif, struct pbuf *p, const struct ieee_802154_addr
 err_t
 lowpan6_set_context(u8_t idx, const ip6_addr_t * context)
 {
-  if (idx > LWIP_6LOWPAN_NUM_CONTEXTS) {
+  if (idx >= LWIP_6LOWPAN_NUM_CONTEXTS) {
     return ERR_ARG;
   }