diff --git a/tests/periph_uart/main.c b/tests/periph_uart/main.c
index 52fbd19871..56b85c9930 100644
--- a/tests/periph_uart/main.c
+++ b/tests/periph_uart/main.c
@@ -63,7 +63,7 @@ static int parse_dev(char *arg)
     return dev;
 }
 
-static void rx_cb(void *arg, char data)
+static void rx_cb(void *arg, uint8_t data)
 {
     int dev = (int)arg;