diff --git a/master/ethernet.c b/master/ethernet.c
index 4dda1fee..09e274b2 100644
--- a/master/ethernet.c
+++ b/master/ethernet.c
@@ -299,7 +299,7 @@ int ec_eoe_send(ec_eoe_t *eoe /**< EoE handler */)
 #endif
 
     data = ec_slave_mbox_prepare_send(eoe->slave, &eoe->datagram,
-            0x02, current_size + 4);
+            EC_MBOX_TYPE_EOE, current_size + 4);
     if (IS_ERR(data))
         return PTR_ERR(data);
 
@@ -478,7 +478,7 @@ void ec_eoe_state_rx_fetch(ec_eoe_t *eoe /**< EoE handler */)
         return;
     }
 
-    if (mbox_prot != 0x02) { // EoE FIXME mailbox handler necessary
+    if (mbox_prot != EC_MBOX_TYPE_EOE) { // FIXME mailbox handler necessary
         eoe->stats.rx_errors++;
 #if EOE_DEBUG_LEVEL >= 1
         EC_SLAVE_WARN(eoe->slave, "Other mailbox protocol response for %s.\n",
diff --git a/master/fsm_coe.c b/master/fsm_coe.c
index cea0b023..b3116b6a 100644
--- a/master/fsm_coe.c
+++ b/master/fsm_coe.c
@@ -318,7 +318,8 @@ int ec_fsm_coe_prepare_dict(
         )
 {
     ec_slave_t *slave = fsm->slave;
-    uint8_t *data = ec_slave_mbox_prepare_send(slave, datagram, 0x03, 8);
+    uint8_t *data = ec_slave_mbox_prepare_send(slave, datagram,
+			EC_MBOX_TYPE_COE, 8);
     if (IS_ERR(data)) {
         return PTR_ERR(data);
     }
@@ -470,7 +471,8 @@ int ec_fsm_coe_dict_prepare_desc(
         )
 {
     ec_slave_t *slave = fsm->slave;
-    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, 0x03, 8);
+    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
+			8);
     if (IS_ERR(data)) {
         return PTR_ERR(data);
     }
@@ -532,7 +534,7 @@ void ec_fsm_coe_dict_response(
         return;
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
                 mbox_prot);
         fsm->state = ec_fsm_coe_error;
@@ -752,7 +754,8 @@ int ec_fsm_coe_dict_prepare_entry(
         )
 {
     ec_slave_t *slave = fsm->slave;
-    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, 0x03, 10);
+    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
+			10);
     if (IS_ERR(data)) {
         return PTR_ERR(data);
     }
@@ -813,7 +816,7 @@ void ec_fsm_coe_dict_desc_response(
         return;
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
                 mbox_prot);
         fsm->state = ec_fsm_coe_error;
@@ -1049,7 +1052,7 @@ void ec_fsm_coe_dict_entry_response(
         return;
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         EC_SLAVE_ERR(slave, "Received mailbox protocol"
                 " 0x%02X as response.\n", mbox_prot);
         fsm->state = ec_fsm_coe_error;
@@ -1200,7 +1203,7 @@ int ec_fsm_coe_prepare_down_start(
     uint8_t data_set_size;
 
     if (request->data_size <= 4) { // use expedited transfer type
-        data = ec_slave_mbox_prepare_send(slave, datagram, 0x03,
+        data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
                 EC_COE_DOWN_REQ_HEADER_SIZE);
         if (IS_ERR(data)) {
             request->errno = PTR_ERR(data);
@@ -1241,7 +1244,7 @@ int ec_fsm_coe_prepare_down_start(
             data_size = required_data_size;
         }
 
-        data = ec_slave_mbox_prepare_send(slave, datagram, 0x03,
+        data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
                 data_size);
         if (IS_ERR(data)) {
             request->errno = PTR_ERR(data);
@@ -1491,7 +1494,7 @@ void ec_fsm_coe_down_prepare_segment_request(
             + EC_COE_DOWN_SEG_MIN_DATA_SIZE;
     }
 
-    data = ec_slave_mbox_prepare_send(slave, datagram, 0x03,
+    data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
             data_size);
     if (IS_ERR(data)) {
         request->errno = PTR_ERR(data);
@@ -1565,7 +1568,7 @@ void ec_fsm_coe_down_response(
         return;
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         request->errno = EIO;
         fsm->state = ec_fsm_coe_error;
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
@@ -1743,7 +1746,7 @@ void ec_fsm_coe_down_seg_response(
         return;
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         request->errno = EIO;
         fsm->state = ec_fsm_coe_error;
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
@@ -1844,7 +1847,8 @@ int ec_fsm_coe_prepare_up(
     ec_sdo_request_t *request = fsm->request;
     ec_master_t *master = slave->master;
 
-    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, 0x03, 10);
+    u8 *data = ec_slave_mbox_prepare_send(slave, datagram, EC_MBOX_TYPE_COE,
+			10);
     if (IS_ERR(data)) {
         request->errno = PTR_ERR(data);
         return PTR_ERR(data);
@@ -2035,7 +2039,8 @@ void ec_fsm_coe_up_prepare_segment_request(
         )
 {
     uint8_t *data =
-        ec_slave_mbox_prepare_send(fsm->slave, datagram, 0x03, 10);
+        ec_slave_mbox_prepare_send(fsm->slave, datagram, EC_MBOX_TYPE_COE,
+				10);
     if (IS_ERR(data)) {
         fsm->request->errno = PTR_ERR(data);
         fsm->state = ec_fsm_coe_error;
@@ -2108,7 +2113,7 @@ void ec_fsm_coe_up_response(
         ec_print_data(data, rec_size);
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         request->errno = EIO;
         fsm->state = ec_fsm_coe_error;
         EC_SLAVE_WARN(slave, "Received mailbox protocol 0x%02X"
@@ -2413,7 +2418,7 @@ void ec_fsm_coe_up_seg_response(
         ec_print_data(data, rec_size);
     }
 
-    if (mbox_prot != 0x03) { // CoE
+    if (mbox_prot != EC_MBOX_TYPE_COE) {
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
                 mbox_prot);
         request->errno = EIO;
diff --git a/master/fsm_foe.c b/master/fsm_foe.c
index 2e889699..b0f379a1 100644
--- a/master/fsm_foe.c
+++ b/master/fsm_foe.c
@@ -46,10 +46,6 @@
  */
 #define EC_FSM_FOE_TIMEOUT 3000
 
-/** Mailbox type FoE.
- */
-#define EC_MBOX_TYPE_FILEACCESS 0x04
-
 /** Size of the FoE header.
  */
 #define EC_FOE_HEADER_SIZE 6
@@ -253,8 +249,7 @@ int ec_foe_prepare_data_send(
     }
 
     data = ec_slave_mbox_prepare_send(fsm->slave,
-            datagram, EC_MBOX_TYPE_FILEACCESS,
-            current_size + EC_FOE_HEADER_SIZE);
+            datagram, EC_MBOX_TYPE_FOE, current_size + EC_FOE_HEADER_SIZE);
     if (IS_ERR(data)) {
         return -1;
     }
@@ -291,7 +286,7 @@ int ec_foe_prepare_wrq_send(
     current_size = fsm->tx_filename_len;
 
     data = ec_slave_mbox_prepare_send(fsm->slave, datagram,
-            EC_MBOX_TYPE_FILEACCESS, current_size + EC_FOE_HEADER_SIZE);
+            EC_MBOX_TYPE_FOE, current_size + EC_FOE_HEADER_SIZE);
     if (IS_ERR(data)) {
         return -1;
     }
@@ -428,7 +423,7 @@ void ec_fsm_foe_state_ack_read(
         return;
     }
 
-    if (mbox_prot != EC_MBOX_TYPE_FILEACCESS) { // FoE
+    if (mbox_prot != EC_MBOX_TYPE_FOE) {
         ec_foe_set_tx_error(fsm, FOE_MBOX_PROT_ERROR);
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
                 mbox_prot);
@@ -563,7 +558,7 @@ int ec_foe_prepare_rrq_send(
     current_size = fsm->rx_filename_len;
 
     data = ec_slave_mbox_prepare_send(fsm->slave, datagram,
-            EC_MBOX_TYPE_FILEACCESS, current_size + EC_FOE_HEADER_SIZE);
+            EC_MBOX_TYPE_FOE, current_size + EC_FOE_HEADER_SIZE);
     if (IS_ERR(data)) {
         return -1;
     }
@@ -594,7 +589,7 @@ int ec_foe_prepare_send_ack(
     uint8_t *data;
 
     data = ec_slave_mbox_prepare_send(fsm->slave, datagram,
-            EC_MBOX_TYPE_FILEACCESS, EC_FOE_HEADER_SIZE);
+            EC_MBOX_TYPE_FOE, EC_FOE_HEADER_SIZE);
     if (IS_ERR(data)) {
         return -1;
     }
@@ -767,7 +762,7 @@ void ec_fsm_foe_state_data_read(
         return;
     }
 
-    if (mbox_prot != EC_MBOX_TYPE_FILEACCESS) { // FoE
+    if (mbox_prot != EC_MBOX_TYPE_FOE) {
         EC_SLAVE_ERR(slave, "Received mailbox protocol 0x%02X as response.\n",
                 mbox_prot);
         ec_foe_set_rx_error(fsm, FOE_PROT_ERROR);
diff --git a/master/fsm_soe.c b/master/fsm_soe.c
index 53b8ac6e..b21846e7 100644
--- a/master/fsm_soe.c
+++ b/master/fsm_soe.c
@@ -41,10 +41,6 @@
 
 /*****************************************************************************/
 
-/** Mailbox type for SoE.
- */
-#define EC_MBOX_TYPE_SOE 0x05
-
 /** SoE operations
  */
 enum ec_soe_opcodes {
diff --git a/master/mailbox.h b/master/mailbox.h
index cdd2eb25..db130ff1 100644
--- a/master/mailbox.h
+++ b/master/mailbox.h
@@ -45,6 +45,16 @@
  */
 #define EC_MBOX_HEADER_SIZE 6
 
+/** Mailbox types.
+ */
+enum ec_mbox_types {
+    EC_MBOX_TYPE_EOE = 0x02,
+    EC_MBOX_TYPE_COE = 0x03,
+    EC_MBOX_TYPE_FOE = 0x04,
+    EC_MBOX_TYPE_SOE = 0x05,
+    EC_MBOX_TYPE_VOE = 0x0f,
+};
+
 /*****************************************************************************/
 
 uint8_t *ec_slave_mbox_prepare_send(const ec_slave_t *, ec_datagram_t *,
diff --git a/master/voe_handler.c b/master/voe_handler.c
index 6ad1fc41..6e0a39b1 100644
--- a/master/voe_handler.c
+++ b/master/voe_handler.c
@@ -40,10 +40,6 @@
 #include "mailbox.h"
 #include "voe_handler.h"
 
-/** VoE mailbox type.
- */
-#define EC_MBOX_TYPE_VOE 0x0f
-
 /** VoE header size.
  */
 #define EC_VOE_HEADER_SIZE 6