diff --git a/src/tetra_mac_pdu.c b/src/tetra_mac_pdu.c
index b525dca..58a8845 100644
--- a/src/tetra_mac_pdu.c
+++ b/src/tetra_mac_pdu.c
@@ -23,6 +23,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
+#include <errno.h>
 
 #include <osmocom/core/utils.h>
 
@@ -140,6 +141,28 @@ static int decode_nr_slots(uint8_t in)
 	return dec_tbl[in & 0xf];
 }
 
+#define MACPDU_LEN_2ND_STOLEN	-1
+#define MACPDU_LEN_START_FRAG	-2
+
+static int decode_length(unsigned int length_ind)
+{
+	/* FIXME: Y2/Z2 for non-pi4 DQPSK */
+	unsigned int y2 = 1, z2 = 1;
+
+	if (length_ind == 0 || length_ind == 0x3b || length_ind == 0x3c)
+		return -EINVAL;
+	else if (length_ind <= 0x12)
+		return y2 * length_ind;
+	else if (length_ind <= 0x3a)
+		return (18 * y2 + (length_ind - 18) * z2);
+	else if (length_ind == 0x3e)
+		return MACPDU_LEN_2ND_STOLEN;
+	else if (length_ind == 0x3f)
+		return MACPDU_LEN_START_FRAG;
+	else
+		return -EINVAL;
+}
+
 /* Section 21.4.3.1 MAC-RESOURCE */
 int macpdu_decode_resource(struct tetra_resrc_decoded *rsd, const uint8_t *bits)
 {
@@ -147,8 +170,7 @@ int macpdu_decode_resource(struct tetra_resrc_decoded *rsd, const uint8_t *bits)
 
 	rsd->encryption_mode = bits_to_uint(cur, 2); cur += 2;
 	rsd->rand_acc_flag = *cur++;
-	/* FIXME: Y2/... octet calculation */
-	rsd->length_ind = bits_to_uint(cur, 6); cur += 6;
+	rsd->macpdu_length = decode_length(bits_to_uint(cur, 6)); cur += 6;
 	rsd->addr.type = bits_to_uint(cur, 3); cur += 3;
 	switch (rsd->addr.type) {
 	case ADDR_TYPE_NULL:
diff --git a/src/tetra_mac_pdu.h b/src/tetra_mac_pdu.h
index 3360938..74608a6 100644
--- a/src/tetra_mac_pdu.h
+++ b/src/tetra_mac_pdu.h
@@ -202,7 +202,7 @@ struct tetra_addr {
 struct tetra_resrc_decoded {
 	uint8_t encryption_mode;
 	uint8_t rand_acc_flag;
-	uint8_t length_ind;
+	int macpdu_length;
 	struct tetra_addr addr;
 
 	uint8_t power_control_pres;
diff --git a/src/tetra_upper_mac.c b/src/tetra_upper_mac.c
index bb5812a..a493bab 100644
--- a/src/tetra_upper_mac.c
+++ b/src/tetra_upper_mac.c
@@ -114,8 +114,8 @@ static void rx_resrc(struct tetra_tmvsap_prim *tmvp)
 	memset(&rsd, 0, sizeof(rsd));
 	tmpdu_offset = macpdu_decode_resource(&rsd, tup->mac_block);
 
-	printf("RESOURCE Encr=%u, Length_ind=%u Addr=%s ",
-		rsd.encryption_mode, rsd.length_ind,
+	printf("RESOURCE Encr=%u, Length=%d Addr=%s ",
+		rsd.encryption_mode, rsd.macpdu_length,
 		tetra_addr_dump(&rsd.addr));
 
 	if (rsd.chan_alloc_pres)
@@ -125,8 +125,8 @@ static void rx_resrc(struct tetra_tmvsap_prim *tmvp)
 		printf("SlotGrant=%u/%u\n", rsd.slot_granting.nr_slots,
 			rsd.slot_granting.delay);
 
-	if (rsd.length_ind && rsd.encryption_mode == 0) {
-		int len_bits = rsd.length_ind*8;
+	if (rsd.macpdu_length > 0 && rsd.encryption_mode == 0) {
+		int len_bits = rsd.macpdu_length*8;
 		if (tup->mac_block + tmpdu_offset + len_bits >
 					tup->mac_block + tup->mac_block_len)
 			len_bits = tup->mac_block_len - tmpdu_offset;