diff --git a/main.c b/main.c
index acfd7a4..adbd0d3 100644
--- a/main.c
+++ b/main.c
@@ -25,7 +25,7 @@ typedef struct Packet {
     uint8_t ext;
 } packet_t;
 
-void marshal(packet_t *p, uint8_t *data) {
+void marshal(packet_t *p, const uint8_t *data) {
     ((dataStruct_t *) data)->senderID = p->senderID;
     ((dataStruct_t *) data)->packetType = p->packetType;
     ((dataStruct_t *) data)->altitude = p->altitude;
@@ -50,7 +50,7 @@ void marshal(packet_t *p, uint8_t *data) {
     ((dataStruct_t *) data)->ext = p->ext;
 }
 
-void unmarshal(uint8_t *data, packet_t *p) {
+void unmarshal(const uint8_t *data, packet_t *p) {
     p->senderID = ((dataStruct_t *) data)->senderID;
     p->packetType = ((dataStruct_t *) data)->packetType;
     p->altitude = ((dataStruct_t *) data)->altitude;