diff --git a/src/misc/pv/timer.h b/src/misc/pv/timer.h
index 8d1f802..be87b92 100644
--- a/src/misc/pv/timer.h
+++ b/src/misc/pv/timer.h
@@ -75,6 +75,8 @@ public:
      */
     Timer(std::string threadName, ThreadPriority priority);
     virtual ~Timer();
+    //! Prevent new callbacks from being scheduled, and cancel pending callbacks
+    void close();
     /**
      * schedule a callback after a delay.
      * @param timerCallback the timerCallback instance.
diff --git a/src/misc/timer.cpp b/src/misc/timer.cpp
index de9587d..105d491 100644
--- a/src/misc/timer.cpp
+++ b/src/misc/timer.cpp
@@ -160,8 +160,14 @@ void Timer::run()
 }
 
 Timer::~Timer() {
+    close();
+}
+
+void Timer::close() {
     {
          Lock xx(mutex);
+         if(!alive)
+             return; // already closed
          alive = false;
     }
     waitForWork.signal();