diff --git a/drivers/encx24j600/encx24j600.c b/drivers/encx24j600/encx24j600.c
index 4429a007dc..0e158a39f6 100644
--- a/drivers/encx24j600/encx24j600.c
+++ b/drivers/encx24j600/encx24j600.c
@@ -50,7 +50,7 @@
 #define TX_BUFFER_END           (RX_BUFFER_START)
 #define TX_BUFFER_START         (TX_BUFFER_END - TX_BUFFER_LEN)
 
-static void cmd(encx24j600_t *dev, char cmd);
+static void cmd(encx24j600_t *dev, uint8_t cmd);
 static void reg_set(encx24j600_t *dev, uint8_t reg, uint16_t value);
 static uint16_t reg_get(encx24j600_t *dev, uint8_t reg);
 static void reg_clear_bits(encx24j600_t *dev, uint8_t reg, uint16_t mask);
@@ -163,8 +163,8 @@ static void phy_reg_set(encx24j600_t *dev, uint8_t reg, uint16_t value) {
     reg_set(dev, ENC_MIWR, value);
 }
 
-static void cmd(encx24j600_t *dev, char cmd) {
-    spi_transfer_byte(dev->spi, dev->cs, false, (uint8_t)cmd);
+static void cmd(encx24j600_t *dev, uint8_t cmd) {
+    spi_transfer_byte(dev->spi, dev->cs, false, cmd);
 }
 
 static void cmdn(encx24j600_t *dev, uint8_t cmd, char *out, char *in, int len) {