diff --git a/sys/net/gnrc/network_layer/sixlowpan/frag/rbuf.c b/sys/net/gnrc/network_layer/sixlowpan/frag/rbuf.c
index 1203fc12b7..fc2d16bacc 100644
--- a/sys/net/gnrc/network_layer/sixlowpan/frag/rbuf.c
+++ b/sys/net/gnrc/network_layer/sixlowpan/frag/rbuf.c
@@ -87,11 +87,16 @@ static int _rbuf_add(gnrc_netif_hdr_t *netif_hdr, gnrc_pktsnip_t *pkt,
                      size_t offset, unsigned page)
 {
     rbuf_t *entry;
-    sixlowpan_frag_t *frag = pkt->data;
+    sixlowpan_frag_n_t *frag = pkt->data;
     rbuf_int_t *ptr;
     uint8_t *data = ((uint8_t *)pkt->data) + sizeof(sixlowpan_frag_t);
     size_t frag_size;
 
+    /* check if provided offset is the same as in fragment */
+    assert(((((frag->disp_size.u8[0] & SIXLOWPAN_FRAG_DISP_MASK) ==
+                SIXLOWPAN_FRAG_1_DISP)) && (offset == 0)) ||
+           ((((frag->disp_size.u8[0] & SIXLOWPAN_FRAG_DISP_MASK) ==
+                SIXLOWPAN_FRAG_N_DISP)) && (offset == (frag->offset * 8U))));
     rbuf_gc();
     entry = _rbuf_get(gnrc_netif_hdr_get_src_addr(netif_hdr), netif_hdr->src_l2addr_len,
                       gnrc_netif_hdr_get_dst_addr(netif_hdr), netif_hdr->dst_l2addr_len,