diff --git a/drivers/grove/lcd_rgb.c b/drivers/grove/lcd_rgb.c
index 57bef796d9..f81e966771 100644
--- a/drivers/grove/lcd_rgb.c
+++ b/drivers/grove/lcd_rgb.c
@@ -102,7 +102,7 @@ static inline void _sleep(uint32_t sleep_in_ms)
 /********************************************
  *  PUBLIC FUNCTIONS
  *******************************************/
-void glcd_print(struct device *port, unsigned char *data, uint32_t size)
+void glcd_print(struct device *port, char *data, uint32_t size)
 {
 	const struct glcd_driver * const rom = (struct glcd_driver *)
 						port->config->config_info;
diff --git a/include/display/grove_lcd.h b/include/display/grove_lcd.h
index 5884f99834..5f222640cf 100644
--- a/include/display/grove_lcd.h
+++ b/include/display/grove_lcd.h
@@ -20,7 +20,7 @@ extern "C" {
  *  @param data the ASCII text to display
  *  @param size the length of the text in bytes
  */
-void glcd_print(struct device *port, unsigned char *data, uint32_t size);
+void glcd_print(struct device *port, char *data, uint32_t size);
 
 
 /**