diff --git a/core/net/sicslowpan.c b/core/net/sicslowpan.c
index cdbe33fc8..4f5d023a3 100644
--- a/core/net/sicslowpan.c
+++ b/core/net/sicslowpan.c
@@ -200,7 +200,7 @@ static uint8_t rime_hdr_len;
  * headers (can be the IP payload if the IP header only is compressed
  * or the UDP payload if the UDP header is also compressed)
  */
-static uint8_t rime_payload_len;
+static int rime_payload_len;
 
 /**
  * uncomp_hdr_len is the length of the headers before compression (if HC2
@@ -999,9 +999,10 @@ uncompress_hdr_hc06(uint16_t ip_len)
   
   /* IP length field. */
   if(ip_len == 0) {
+    int len = packetbuf_datalen() - rime_hdr_len + uncomp_hdr_len - UIP_IPH_LEN;
     /* This is not a fragmented packet */
-    SICSLOWPAN_IP_BUF->len[0] = 0;
-    SICSLOWPAN_IP_BUF->len[1] = packetbuf_datalen() - rime_hdr_len + uncomp_hdr_len - UIP_IPH_LEN;
+    SICSLOWPAN_IP_BUF->len[0] = len >> 8;
+    SICSLOWPAN_IP_BUF->len[1] = len & 0x00FF;
   } else {
     /* This is a 1st fragment */
     SICSLOWPAN_IP_BUF->len[0] = (ip_len - UIP_IPH_LEN) >> 8;
@@ -1246,9 +1247,10 @@ uncompress_hdr_hc1(uint16_t ip_len)
   
   /* IP length field. */
   if(ip_len == 0) {
+    int len = packetbuf_datalen() - rime_hdr_len + uncomp_hdr_len - UIP_IPH_LEN;
     /* This is not a fragmented packet */
-    SICSLOWPAN_IP_BUF->len[0] = 0;
-    SICSLOWPAN_IP_BUF->len[1] = packetbuf_datalen() - rime_hdr_len + uncomp_hdr_len - UIP_IPH_LEN;
+    SICSLOWPAN_IP_BUF->len[0] = len >> 8;
+    SICSLOWPAN_IP_BUF->len[1] = len & 0x00FF;
   } else {
     /* This is a 1st fragment */
     SICSLOWPAN_IP_BUF->len[0] = (ip_len - UIP_IPH_LEN) >> 8;
@@ -1480,7 +1482,7 @@ output(uip_lladdr_t *localdest)
 
     /* Copy payload and send */
     rime_hdr_len += SICSLOWPAN_FRAG1_HDR_LEN;
-    rime_payload_len = (MAC_MAX_PAYLOAD - framer_hdrlen - rime_hdr_len) & 0xf8;
+    rime_payload_len = (MAC_MAX_PAYLOAD - framer_hdrlen - rime_hdr_len) & 0xfffffff8;
     PRINTFO("(len %d, tag %d)\n", rime_payload_len, my_tag);
     memcpy(rime_ptr + rime_hdr_len,
            (uint8_t *)UIP_IP_BUF + uncomp_hdr_len, rime_payload_len);
@@ -1516,7 +1518,7 @@ output(uip_lladdr_t *localdest)
 /*       uip_htons((SICSLOWPAN_DISPATCH_FRAGN << 8) | uip_len); */
     SET16(RIME_FRAG_PTR, RIME_FRAG_DISPATCH_SIZE,
           ((SICSLOWPAN_DISPATCH_FRAGN << 8) | uip_len));
-    rime_payload_len = (MAC_MAX_PAYLOAD - framer_hdrlen - rime_hdr_len) & 0xf8;
+    rime_payload_len = (MAC_MAX_PAYLOAD - framer_hdrlen - rime_hdr_len) & 0xfffffff8;
     while(processed_ip_out_len < uip_len) {
       PRINTFO("sicslowpan output: fragment ");
       RIME_FRAG_PTR[RIME_FRAG_OFFSET] = processed_ip_out_len >> 3;