diff --git a/core/net/mac/csma.c b/core/net/mac/csma.c
index 82b2980fd..66528e542 100644
--- a/core/net/mac/csma.c
+++ b/core/net/mac/csma.c
@@ -63,6 +63,14 @@
 #define PRINTF(...)
 #endif /* DEBUG */
 
+#ifndef CSMA_MAX_BACKOFF_EXPONENT
+#ifdef CSMA_CONF_MAX_BACKOFF_EXPONENT
+#define CSMA_MAX_BACKOFF_EXPONENT CSMA_CONF_MAX_BACKOFF_EXPONENT
+#else
+#define CSMA_MAX_BACKOFF_EXPONENT 3
+#endif /* CSMA_CONF_MAX_BACKOFF_EXPONENT */
+#endif /* CSMA_MAX_BACKOFF_EXPONENT */
+
 #ifndef CSMA_MAX_MAC_TRANSMISSIONS
 #ifdef CSMA_CONF_MAX_MAC_TRANSMISSIONS
 #define CSMA_MAX_MAC_TRANSMISSIONS CSMA_CONF_MAX_MAC_TRANSMISSIONS
@@ -194,6 +202,7 @@ packet_sent(void *ptr, int status, int num_transmissions)
   mac_callback_t sent;
   void *cptr;
   int num_tx;
+  int backoff_exponent;
   int backoff_transmissions;
 
   n = ptr;
@@ -249,18 +258,21 @@ packet_sent(void *ptr, int status, int num_transmissions)
            check interval of the underlying radio duty cycling layer. */
         time = default_timebase();
 
-        /* The retransmission time uses a linear backoff so that the
-           interval between the transmissions increase with each
-           retransmit. */
-        backoff_transmissions = n->transmissions + 1;
+        /* The retransmission time uses a truncated exponential backoff
+         * so that the interval between the transmissions increase with
+         * each retransmit. */
+        backoff_exponent = num_tx;
 
-        /* Clamp the number of backoffs so that we don't get a too long
-           timeout here, since that will delay all packets in the
-           queue. */
-        if(backoff_transmissions > 3) {
-          backoff_transmissions = 3;
+        /* Truncate the exponent if needed. */
+        if(backoff_exponent > CSMA_MAX_BACKOFF_EXPONENT) {
+          backoff_exponent = CSMA_MAX_BACKOFF_EXPONENT;
         }
 
+        /* Proceed to exponentiation. */
+        backoff_transmissions = 1 << backoff_exponent;
+
+        /* Pick a time for next transmission, within the interval:
+         * [time, time + 2^backoff_exponent * time[ */
         time = time + (random_rand() % (backoff_transmissions * time));
 
         if(n->transmissions < metadata->max_transmissions) {