diff --git a/src/core/fv-trace-source.h b/src/core/fv-trace-source.h
index f305980a5..5b9f44df4 100644
--- a/src/core/fv-trace-source.h
+++ b/src/core/fv-trace-source.h
@@ -40,10 +40,10 @@ public:
 
   ~FVTraceSourceBase () {}
 
-  void AddCallback (CallbackBase const & callback, TraceContext const & context) {
+  virtual void AddCallback (CallbackBase const & callback, TraceContext const & context) {
     m_callback.AddCallback (callback, context);
   }
-  void RemoveCallback (CallbackBase const & callback) {
+  virtual void RemoveCallback (CallbackBase const & callback) {
     m_callback.RemoveCallback (callback);
   }
 protected:
diff --git a/src/core/sv-trace-source.h b/src/core/sv-trace-source.h
index d7038c0ad..7c2bd8818 100644
--- a/src/core/sv-trace-source.h
+++ b/src/core/sv-trace-source.h
@@ -40,10 +40,10 @@ public:
 
   virtual ~SVTraceSourceBase () {}
 
-  void AddCallback (CallbackBase const & callback, TraceContext const & context) {
+  virtual void AddCallback (CallbackBase const & callback, TraceContext const & context) {
     m_callback.AddCallback (callback, context);
   }
-  void RemoveCallback (CallbackBase const & callback) {
+  virtual void RemoveCallback (CallbackBase const & callback) {
     m_callback.RemoveCallback (callback);
   }
 protected:
diff --git a/src/core/uv-trace-source.h b/src/core/uv-trace-source.h
index 2216f2c98..55602e614 100644
--- a/src/core/uv-trace-source.h
+++ b/src/core/uv-trace-source.h
@@ -43,10 +43,10 @@ public:
   }
   ~UVTraceSourceBase () {}
 
-  void AddCallback (CallbackBase const & callback, TraceContext const & context) {
+  virtual void AddCallback (CallbackBase const & callback, TraceContext const & context) {
     m_callback.AddCallback (callback, context);
   }
-  void RemoveCallback (CallbackBase const & callback) {
+  virtual void RemoveCallback (CallbackBase const & callback) {
     m_callback.RemoveCallback (callback);
   }