diff --git a/src/modules/syslink/syslink.c b/src/modules/syslink/syslink.c
index 303ba7fc02..9018e07a0d 100644
--- a/src/modules/syslink/syslink.c
+++ b/src/modules/syslink/syslink.c
@@ -118,7 +118,7 @@ int syslink_parse_char(syslink_parse_state *state, char c, syslink_message_t *ms
 
 		state->index++;
 
-		if (state->index >= sizeof(msg->cksum)) {
+		if (state->index >= (int)sizeof(msg->cksum)) {
 			state->state = SYSLINK_STATE_START;
 			state->index = 0;
 			return 1;
diff --git a/src/modules/syslink/syslink_main.cpp b/src/modules/syslink/syslink_main.cpp
index 5e4ceb0bbb..b82e342fd1 100644
--- a/src/modules/syslink/syslink_main.cpp
+++ b/src/modules/syslink/syslink_main.cpp
@@ -705,7 +705,7 @@ Syslink::send_bytes(const void *data, size_t len)
 	// TODO: This could be way more efficient
 	//       Using interrupts/DMA/polling would be much better
 
-	for (int i = 0; i < len; i++) {
+	for (size_t i = 0; i < len; i++) {
 		// Block until we can send a byte
 		while (px4_arch_gpioread(GPIO_NRF_TXEN)) ;
 
@@ -804,7 +804,7 @@ void status()
 		printf(", VID: %02X , PID: %02X\n", desc.header, desc.vendorId, desc.productId);
 
 		// Print pages of memory
-		for (int di = 0; di < sizeof(desc); di++) {
+		for (size_t di = 0; di < sizeof(desc); di++) {
 			if (di % 16 == 0) {
 				printf("\n");
 			}