diff --git a/boards/chronos/board_init.c b/boards/chronos/board_init.c
index ab94cf2024..b3c189f7fe 100644
--- a/boards/chronos/board_init.c
+++ b/boards/chronos/board_init.c
@@ -1,7 +1,9 @@
 #include <stdint.h>
+
 #include "board.h"
 #include "cpu.h"
 #include "irq.h"
+#include "debug.h"
 
 #include "display.h"
 #include "display_putchar.h"
diff --git a/boards/chronos/drivers/battery.c b/boards/chronos/drivers/battery.c
index 30f788d9fb..e787f868b9 100644
--- a/boards/chronos/drivers/battery.c
+++ b/boards/chronos/drivers/battery.c
@@ -1,5 +1,6 @@
 #include <stdint.h>
 #include <cc430f6137.h>
+
 #include "cc430-adc.h"
 
 uint32_t battery_get_voltage(void)
diff --git a/boards/chronos/drivers/buzzer.c b/boards/chronos/drivers/buzzer.c
index edde080f4c..2cee84e5ea 100644
--- a/boards/chronos/drivers/buzzer.c
+++ b/boards/chronos/drivers/buzzer.c
@@ -1,5 +1,6 @@
 #include <stdint.h>
 #include <cc430f6137.h>
+
 #include "buzzer.h"
 #include "hwtimer.h"
 
diff --git a/boards/chronos/drivers/display.c b/boards/chronos/drivers/display.c
index 87705d1206..e0691700cd 100644
--- a/boards/chronos/drivers/display.c
+++ b/boards/chronos/drivers/display.c
@@ -44,6 +44,7 @@
 
 /* driver */
 #include <cc430f6137.h>
+
 #include "display.h"
 
 
diff --git a/boards/chronos/drivers/display1.c b/boards/chronos/drivers/display1.c
index 1c4ee35b21..6b6a4b622c 100644
--- a/boards/chronos/drivers/display1.c
+++ b/boards/chronos/drivers/display1.c
@@ -40,6 +40,7 @@
 /* Include section */
 #include <stdint.h>
 #include <cc430f6137.h>
+
 #include "display.h"
 
 /* ************************************************************************************************* */
diff --git a/boards/chronos/drivers/display_putchar.c b/boards/chronos/drivers/display_putchar.c
index db48d72284..4a57d8e84c 100644
--- a/boards/chronos/drivers/display_putchar.c
+++ b/boards/chronos/drivers/display_putchar.c
@@ -1,8 +1,9 @@
 #include <stdio.h>
 #include <string.h>
+#include <ctype.h>
+
 #include "display.h"
 
-extern int toupper(int c);
 extern void (*_putchar)(int c);
 
 static char display_buf[11];