diff --git a/os/net/mac/csma/csma.h b/os/net/mac/csma/csma.h
index dd5688666..88396db0b 100644
--- a/os/net/mac/csma/csma.h
+++ b/os/net/mac/csma/csma.h
@@ -69,7 +69,7 @@
 #ifdef  CSMA_MAC_CONF_LEN
 #define CSMA_MAC_LEN CSMA_MAC_CONF_LEN
 #else
-#define CSMA_MAC_LEN 127
+#define CSMA_MAC_LEN 127 - 2
 #endif
 
 /* just a default - with LLSEC, etc */
diff --git a/os/net/mac/tsch/tsch-const.h b/os/net/mac/tsch/tsch-const.h
index edc989378..f78b9883d 100644
--- a/os/net/mac/tsch/tsch-const.h
+++ b/os/net/mac/tsch/tsch-const.h
@@ -66,8 +66,8 @@
 /* 1 channel, sequence length 1 */
 #define TSCH_HOPPING_SEQUENCE_1_1 (uint8_t[]){ 20 }
 
-/* Max TSCH packet lenght */
-#define TSCH_PACKET_MAX_LEN MIN(127, PACKETBUF_SIZE)
+/* Max TSCH packet lenght - last bytes are CRC in default 802.15.4 packets */
+#define TSCH_PACKET_MAX_LEN MIN(127 - 2, PACKETBUF_SIZE)
 
 /* The jitter to remove in ticks.
  * This should be the sum of measurement errors on Tx and Rx nodes.
diff --git a/os/net/mac/tsch/tsch.c b/os/net/mac/tsch/tsch.c
index 719a09b9f..8c79c299c 100644
--- a/os/net/mac/tsch/tsch.c
+++ b/os/net/mac/tsch/tsch.c
@@ -62,9 +62,6 @@
 #include "net/mac/tsch/sixtop/sixtop.h"
 #endif
 
-/* Needed to estimate the MAC lenght */
-#define TSCH_MAC_MAX_LEN 127
-
 #if FRAME802154_VERSION < FRAME802154_IEEE802154_2015
 #error TSCH: FRAME802154_VERSION must be at least FRAME802154_IEEE802154_2015
 #endif
@@ -1135,7 +1132,7 @@ static int
 max_payload(void)
 {
   /* Setup security... before. */
-  return TSCH_MAC_MAX_LEN -  NETSTACK_FRAMER.length();
+  return TSCH_PACKET_MAX_LEN -  NETSTACK_FRAMER.length();
 }
 /*---------------------------------------------------------------------------*/
 const struct mac_driver tschmac_driver = {