diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
index 12a96585da949af2891987be45168851c36eab65..a8eb7be189ecdd2a0cbf9d29895e01331dd7076f 100644
--- a/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
+++ b/tools/perf/util/arm-spe-decoder/arm-spe-pkt-decoder.c
@@ -69,22 +69,22 @@ const char *arm_spe_pkt_name(enum arm_spe_pkt_type type)
 	return arm_spe_packet_name[type];
 }
 
-/* return ARM SPE payload size from its encoding,
- * which is in bits 5:4 of the byte.
- * 00 : byte
- * 01 : halfword (2)
- * 10 : word (4)
- * 11 : doubleword (8)
+/*
+ * Extracts the field "sz" from header bits and converts to bytes:
+ *   00 : byte (1)
+ *   01 : halfword (2)
+ *   10 : word (4)
+ *   11 : doubleword (8)
  */
-static int payloadlen(unsigned char byte)
+static unsigned int arm_spe_payload_len(unsigned char hdr)
 {
-	return 1 << ((byte & 0x30) >> 4);
+	return 1U << ((hdr & GENMASK_ULL(5, 4)) >> 4);
 }
 
 static int arm_spe_get_payload(const unsigned char *buf, size_t len,
 			       struct arm_spe_pkt *packet)
 {
-	size_t payload_len = payloadlen(buf[0]);
+	size_t payload_len = arm_spe_payload_len(buf[0]);
 
 	if (len < 1 + payload_len)
 		return ARM_SPE_NEED_MORE_BYTES;