diff --git a/libs/ardour/audio_diskstream.cc b/libs/ardour/audio_diskstream.cc
index f0316894e2..6fe1cdc0a6 100644
--- a/libs/ardour/audio_diskstream.cc
+++ b/libs/ardour/audio_diskstream.cc
@@ -1095,7 +1095,13 @@ AudioDiskstream::_do_refill (Sample* mixdown_buffer, float* gain_buffer)
 	assert(mixdown_buffer);
 	assert(gain_buffer);
 
+	vector.buf[0] = 0;
+	vector.len[0] = 0;
+	vector.buf[1] = 0;
+	vector.len[1] = 0;
+
 	channels.front().playback_buf->get_write_vector (&vector);
+
 	
 	if ((total_space = vector.len[0] + vector.len[1]) == 0) {
 		return 0;
diff --git a/libs/pbd/pbd/rcu.h b/libs/pbd/pbd/rcu.h
index 86cc6e8cab..c9088d51df 100644
--- a/libs/pbd/pbd/rcu.h
+++ b/libs/pbd/pbd/rcu.h
@@ -10,21 +10,23 @@ template<class T>
 class RCUManager
 {
   public:
-	RCUManager (T* new_rcu_value) {
-		m_rcu_value = new boost::shared_ptr<T> (new_rcu_value);
-	}
-	
-	virtual ~RCUManager() { delete m_rcu_value; }
  
-        boost::shared_ptr<T> reader () const { return *((boost::shared_ptr<T> *) g_atomic_pointer_get ((volatile gpointer*) &m_rcu_value)); }
+	RCUManager (T* new_rcu_value) {
+		x.m_rcu_value = new boost::shared_ptr<T> (new_rcu_value);
+	}
+ 
+	virtual ~RCUManager() { delete x.m_rcu_value; }
+ 
+        boost::shared_ptr<T> reader () const { return *((boost::shared_ptr<T> *) g_atomic_pointer_get (&x.gptr)); }
  
 	virtual boost::shared_ptr<T> write_copy () = 0;
 	virtual bool update (boost::shared_ptr<T> new_value) = 0;
 
-	volatile gpointer* pointer() const { return (volatile gpointer*) &m_rcu_value; }
-
   protected:
-	volatile boost::shared_ptr<T>* m_rcu_value;
+	union {
+	    boost::shared_ptr<T>* m_rcu_value;
+	    volatile gpointer gptr;
+	} x;
 };
  
  
@@ -57,7 +59,7 @@ public:
 
 		// store the current 
 
-		current_write_old = (boost::shared_ptr<T>*) RCUManager<T>::m_rcu_value;
+		current_write_old = RCUManager<T>::x.m_rcu_value;
 		
 		boost::shared_ptr<T> new_copy (new T(**current_write_old));
 
@@ -73,7 +75,7 @@ public:
 
 		// update, checking that nobody beat us to it
 
-		bool ret = g_atomic_pointer_compare_and_exchange (RCUManager<T>::pointer(),
+		bool ret = g_atomic_pointer_compare_and_exchange (&RCUManager<T>::x.gptr,
 								  (gpointer) current_write_old,
 								  (gpointer) new_spp);