diff --git a/cpu/ppc4xx/i2c.c b/cpu/ppc4xx/i2c.c
index 3a644a4..be94b57 100644
--- a/cpu/ppc4xx/i2c.c
+++ b/cpu/ppc4xx/i2c.c
@@ -428,7 +428,7 @@
  */
 uchar i2c_reg_read(uchar i2c_addr, uchar reg)
 {
-	char buf;
+	uchar buf;
 
 	i2c_read(i2c_addr, reg, 1, &buf, 1);
 
diff --git a/cpu/ppc4xx/spd_sdram.c b/cpu/ppc4xx/spd_sdram.c
index 48102ef..7c9ac25 100644
--- a/cpu/ppc4xx/spd_sdram.c
+++ b/cpu/ppc4xx/spd_sdram.c
@@ -456,7 +456,7 @@
 
 int spd_read(uint addr)
 {
-	char data[2];
+	uchar data[2];
 
 	if (i2c_read(SPD_EEPROM_ADDRESS, addr, 1, data, 1) == 0)
 		return (int)data[0];