diff --git a/core/net/mac/csma.c b/core/net/mac/csma.c
index 66528e542..b75a812ca 100644
--- a/core/net/mac/csma.c
+++ b/core/net/mac/csma.c
@@ -306,9 +306,16 @@ send_packet(mac_callback_t sent, void *ptr)
 {
   struct rdc_buf_list *q;
   struct neighbor_queue *n;
+  static uint8_t initialized = 0;
   static uint16_t seqno;
   const rimeaddr_t *addr = packetbuf_addr(PACKETBUF_ADDR_RECEIVER);
 
+  if(!initialized) {
+    initialized = 1;
+    /* Initialize the sequence number to a random value as per 802.15.4. */
+    seqno = random_rand();
+  }
+
   if(seqno == 0) {
     /* PACKETBUF_ATTR_MAC_SEQNO cannot be zero, due to a pecuilarity
        in framer-802154.c. */