diff --git a/core/net/mac/csma.c b/core/net/mac/csma.c
index 9bb2ef239..99dc50f5f 100644
--- a/core/net/mac/csma.c
+++ b/core/net/mac/csma.c
@@ -108,6 +108,13 @@ struct neighbor_queue {
 #define CSMA_MAX_NEIGHBOR_QUEUES 2
 #endif /* CSMA_CONF_MAX_NEIGHBOR_QUEUES */
 
+/* The maximum number of pending packet per neighbor */
+#ifdef CSMA_CONF_MAX_PACKET_PER_NEIGHBOR
+#define CSMA_MAX_PACKET_PER_NEIGHBOR CSMA_CONF_MAX_PACKET_PER_NEIGHBOR
+#else
+#define CSMA_MAX_PACKET_PER_NEIGHBOR MAX_QUEUED_PACKETS
+#endif /* CSMA_CONF_MAX_PACKET_PER_NEIGHBOR */
+
 #define MAX_QUEUED_PACKETS QUEUEBUF_NUM
 MEMB(neighbor_memb, struct neighbor_queue, CSMA_MAX_NEIGHBOR_QUEUES);
 MEMB(packet_memb, struct rdc_buf_list, MAX_QUEUED_PACKETS);
@@ -348,49 +355,53 @@ send_packet(mac_callback_t sent, void *ptr)
 
   if(n != NULL) {
     /* Add packet to the neighbor's queue */
-    q = memb_alloc(&packet_memb);
-    if(q != NULL) {
-      q->ptr = memb_alloc(&metadata_memb);
-      if(q->ptr != NULL) {
-	q->buf = queuebuf_new_from_packetbuf();
-	if(q->buf != NULL) {
-	  struct qbuf_metadata *metadata = (struct qbuf_metadata *)q->ptr;
-	  /* Neighbor and packet successfully allocated */
-	  if(packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS) == 0) {
-	    /* Use default configuration for max transmissions */
-	    metadata->max_transmissions = CSMA_MAX_MAC_TRANSMISSIONS;
-	  } else {
-	    metadata->max_transmissions =
-                  packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS);
-	  }
-	  metadata->sent = sent;
-	  metadata->cptr = ptr;
+    if(list_length(n->queued_packet_list) < CSMA_MAX_PACKET_PER_NEIGHBOR) {
+      q = memb_alloc(&packet_memb);
+      if(q != NULL) {
+        q->ptr = memb_alloc(&metadata_memb);
+        if(q->ptr != NULL) {
+          q->buf = queuebuf_new_from_packetbuf();
+          if(q->buf != NULL) {
+            struct qbuf_metadata *metadata = (struct qbuf_metadata *)q->ptr;
+            /* Neighbor and packet successfully allocated */
+            if(packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS) == 0) {
+              /* Use default configuration for max transmissions */
+              metadata->max_transmissions = CSMA_MAX_MAC_TRANSMISSIONS;
+            } else {
+              metadata->max_transmissions =
+                packetbuf_attr(PACKETBUF_ATTR_MAX_MAC_TRANSMISSIONS);
+            }
+            metadata->sent = sent;
+            metadata->cptr = ptr;
 
-	  if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
-	     PACKETBUF_ATTR_PACKET_TYPE_ACK) {
-	    list_push(n->queued_packet_list, q);
-	  } else {
-	    list_add(n->queued_packet_list, q);
-	  }
+            if(packetbuf_attr(PACKETBUF_ATTR_PACKET_TYPE) ==
+               PACKETBUF_ATTR_PACKET_TYPE_ACK) {
+              list_push(n->queued_packet_list, q);
+            } else {
+              list_add(n->queued_packet_list, q);
+            }
 
-          PRINTF("csma: send_packet, queue length %d, free packets %d\n",
-                 list_length(n->queued_packet_list), memb_numfree(&packet_memb));
-	  /* If q is the first packet in the neighbor's queue, send asap */
-	  if(list_head(n->queued_packet_list) == q) {
-	    ctimer_set(&n->transmit_timer, 0, transmit_packet_list, n);
-	  }
-	  return;
-	}
-	memb_free(&metadata_memb, q->ptr);
-	PRINTF("csma: could not allocate queuebuf, dropping packet\n");
+            PRINTF("csma: send_packet, queue length %d, free packets %d\n",
+                   list_length(n->queued_packet_list), memb_numfree(&packet_memb));
+            /* If q is the first packet in the neighbor's queue, send asap */
+            if(list_head(n->queued_packet_list) == q) {
+              ctimer_set(&n->transmit_timer, 0, transmit_packet_list, n);
+            }
+            return;
+          }
+          memb_free(&metadata_memb, q->ptr);
+          PRINTF("csma: could not allocate queuebuf, dropping packet\n");
+        }
+        memb_free(&packet_memb, q);
+        PRINTF("csma: could not allocate queuebuf, dropping packet\n");
       }
-      memb_free(&packet_memb, q);
-      PRINTF("csma: could not allocate queuebuf, dropping packet\n");
-    }
-    /* The packet allocation failed. Remove and free neighbor entry if empty. */
-    if(list_length(n->queued_packet_list) == 0) {
-      list_remove(neighbor_list, n);
-      memb_free(&neighbor_memb, n);
+      /* The packet allocation failed. Remove and free neighbor entry if empty. */
+      if(list_length(n->queued_packet_list) == 0) {
+        list_remove(neighbor_list, n);
+        memb_free(&neighbor_memb, n);
+      }
+    } else {
+      PRINTF("csma: Neighbor queue full\n");
     }
     PRINTF("csma: could not allocate packet, dropping packet\n");
   } else {