diff --git a/include/timer.h b/include/timer.h
index 71f36c6..e48ee93 100644
--- a/include/timer.h
+++ b/include/timer.h
@@ -5,6 +5,9 @@
  * Based on "From C to C++ course - 2002"
 */
 
+#ifndef __TIMER_H__
+#define __TIMER_H__
+
 void timerInit(int valueMilliSec);
 
 void timerDestroy();
@@ -14,3 +17,5 @@ void timerUpdateTimer(int valueMilliSec);
 int timerTimeOver();
 
 void timerPrint();
+
+#endif /* __TIMER_H__ */