diff --git a/sys/can/conn/raw.c b/sys/can/conn/raw.c
index e8de7b40d0..47a791dac4 100644
--- a/sys/can/conn/raw.c
+++ b/sys/can/conn/raw.c
@@ -72,10 +72,10 @@ int conn_can_raw_set_filter(conn_can_raw_t *conn, struct can_filter *filter, siz
     assert(conn != NULL);
     assert(filter != NULL || count == 0);
 
-    DEBUG("conn_can_raw_set_filter: conn=%p, filter=%p, count=%d\n",
-          (void *)conn, (void *)filter, count);
-    DEBUG("conn_can_raw_set_filter: conn->filter=%p, conn->count=%d\n",
-          (void *)conn->filter, conn->count);
+    DEBUG("conn_can_raw_set_filter: conn=%p, filter=%p, count=%u\n",
+          (void *)conn, (void *)filter, (unsigned)count);
+    DEBUG("conn_can_raw_set_filter: conn->filter=%p, conn->count=%u\n",
+          (void *)conn->filter, (unsigned)conn->count);
 
     /* unset previous filters */
     if (conn->count) {
diff --git a/sys/can/isotp/isotp.c b/sys/can/isotp/isotp.c
index 319ce09141..3de2401189 100644
--- a/sys/can/isotp/isotp.c
+++ b/sys/can/isotp/isotp.c
@@ -509,7 +509,7 @@ static void _isotp_fill_dataframe(struct isotp *isotp, struct can_frame *frame,
     frame->can_id = isotp->opt.tx_id;
     frame->can_dlc = num_bytes + pci_len;
 
-    DEBUG("_isotp_fill_dataframe: num_bytes=%d, pci_len=%d\n", num_bytes, pci_len);
+    DEBUG("_isotp_fill_dataframe: num_bytes=%d, pci_len=%d\n", (unsigned)num_bytes, (unsigned)pci_len);
 
     if (num_bytes < space) {
         if (isotp->opt.flags & CAN_ISOTP_TX_PADDING) {