diff --git a/application.c b/application.c
index 880e480..4d4a108 100644
--- a/application.c
+++ b/application.c
@@ -71,7 +71,7 @@ static time_t time_start = 0;
 /** @defgroup main_flags flag set in interrupts to be processed in main task
  *  @{
  */
-volatile bool rtc_internal_tick_flag = false; /**< flag set when internal RTC ticked */
+static volatile bool rtc_internal_tick_flag = false; /**< flag set when internal RTC ticked */
 /** @} */
 
 size_t putc(char c)