diff --git a/common/rfb/Timer.h b/common/rfb/Timer.h
index e295b82..78687d1 100644
--- a/common/rfb/Timer.h
+++ b/common/rfb/Timer.h
@@ -49,6 +49,8 @@
       //   appropriate interval.
       //   If the handler returns false then the Timer is cancelled.
       virtual bool handleTimeout(Timer* t) = 0;
+
+      virtual ~Callback() {}
     };
 
     // checkTimeouts()