diff --git a/src/Timer.cpp b/src/Timer.cpp
index b2b86dc..ad4397b 100644
--- a/src/Timer.cpp
+++ b/src/Timer.cpp
@@ -70,6 +70,13 @@ bool Timer::setTimer( timer_t timerId,
                       const time_t initExpr_sec,
                       const long initExpr_nsec )
 {
+  if (m_timerUsers.find(timerId) == m_timerUsers.end() ) {
+    LOG_BEGIN(Logger::ERR)
+      LOG_SPROP(timerId)
+    LOG_END("TimerId is not in the map.");
+    return false;
+  }
+
   itimerspec its;
   its.it_value.tv_sec = interval_sec;
   its.it_value.tv_nsec = interval_nsec;
diff --git a/test/test_Timer.hpp b/test/test_Timer.hpp
index 9a75e1c..8c8592b 100644
--- a/test/test_Timer.hpp
+++ b/test/test_Timer.hpp
@@ -185,4 +185,14 @@ private:
     TS_ASSERT_EQUALS(timer.stopTimer( timerId ), false);
   }
 
+  void testSetTimerWhichIsNotInTheMap()
+  {
+    TEST_HEADER;
+
+    Timer timer;
+
+    timer_t timerId = (void*)1234;
+    TS_ASSERT_EQUALS(timer.setTimer( timerId, 1 ), false);
+  }
+
 };