diff --git a/libs/ardour/ardour/audiosource.h b/libs/ardour/ardour/audiosource.h
index 7ea7260688..36c79f6787 100644
--- a/libs/ardour/ardour/audiosource.h
+++ b/libs/ardour/ardour/audiosource.h
@@ -60,7 +60,7 @@ class AudioSource : virtual public Source,
 
 	virtual float sample_rate () const = 0;
 
-	virtual void mark_streaming_write_completed () {}
+	virtual void mark_streaming_write_completed ();
 
 	virtual bool can_truncate_peaks() const { return true; }
 
@@ -111,8 +111,6 @@ class AudioSource : virtual public Source,
 	static bool _build_peakfiles;
 
 	framecnt_t           _length;
-	bool                 _peaks_built;
-	mutable Glib::Mutex  _peaks_ready_lock;
 	std::string         peakpath;
 	std::string        _captured_for;
 
@@ -142,6 +140,15 @@ class AudioSource : virtual public Source,
 				     framecnt_t frames_per_peak);
 
   private:
+	bool _peaks_built;
+	/** This mutex is used to protect both the _peaks_built
+	 *  variable and also the emission (and handling) of the
+	 *  PeaksReady signal.  Holding the lock when emitting
+	 *  PeaksReady means that _peaks_built cannot be changed
+	 *  during the handling of the signal.
+	 */
+	mutable Glib::Mutex _peaks_ready_lock;
+	
 	PBD::FdFileDescriptor* _peakfile_descriptor;
 	int        _peakfile_fd;
 	framecnt_t peak_leftover_cnt;
diff --git a/libs/ardour/audiofilesource.cc b/libs/ardour/audiofilesource.cc
index d3e050e4ba..30f8f84a5b 100644
--- a/libs/ardour/audiofilesource.cc
+++ b/libs/ardour/audiofilesource.cc
@@ -142,7 +142,6 @@ AudioFileSource::~AudioFileSource ()
 int
 AudioFileSource::init (const string& pathstr, bool must_exist)
 {
-	_peaks_built = false;
 	return FileSource::init (pathstr, must_exist);
 }
 
@@ -287,15 +286,7 @@ AudioFileSource::mark_streaming_write_completed ()
 		return;
 	}
 
-	/* XXX notice that we're readers of _peaks_built
-	   but we must hold a solid lock on PeaksReady.
-	*/
-
-	Glib::Mutex::Lock lm (_lock);
-
-	if (_peaks_built) {
-		PeaksReady (); /* EMIT SIGNAL */
-	}
+	AudioSource::mark_streaming_write_completed ();
 }
 
 int
diff --git a/libs/ardour/audiosource.cc b/libs/ardour/audiosource.cc
index 9af388c1cd..360e4cd48a 100644
--- a/libs/ardour/audiosource.cc
+++ b/libs/ardour/audiosource.cc
@@ -165,10 +165,6 @@ AudioSource::peaks_ready (boost::function<void()> doThisWhenReady, ScopedConnect
 	bool ret;
 	Glib::Mutex::Lock lm (_peaks_ready_lock);
 
-	/* check to see if the peak data is ready. if not
-	   connect the slot while still holding the lock.
-	*/
-
 	if (!(ret = _peaks_built)) {
 		*connect_here_if_not = new ScopedConnection;
 		PeaksReady.connect (**connect_here_if_not, MISSING_INVALIDATOR, doThisWhenReady, event_loop);
@@ -683,13 +679,7 @@ AudioSource::build_peaks_from_scratch ()
 		}
 
 		done_with_peakfile_writes ((cnt == 0));
-	}
-
-	{
-		Glib::Mutex::Lock lm (_peaks_ready_lock);
-
-		if (_peaks_built) {
-			PeaksReady (); /* EMIT SIGNAL */
+		if (cnt == 0) {
 			ret = 0;
 		}
 	}
@@ -723,7 +713,9 @@ AudioSource::done_with_peakfile_writes (bool done)
 	}
 
 	if (done) {
+		Glib::Mutex::Lock lm (_peaks_ready_lock);
 		_peaks_built = true;
+		PeaksReady (); /* EMIT SIGNAL */
 	}
 
 	delete _peakfile_descriptor;
@@ -955,3 +947,13 @@ AudioSource::dec_read_data_count (nframes_t cnt)
                 _read_data_count = 0;
         }
 }
+
+void
+AudioSource::mark_streaming_write_completed ()
+{
+	Glib::Mutex::Lock lm (_peaks_ready_lock);
+
+	if (_peaks_built) {
+		PeaksReady (); /* EMIT SIGNAL */
+	}
+}