diff --git a/libs/ardour/ardour/audio_port.h b/libs/ardour/ardour/audio_port.h
index bf4b8efe1e..c9eaab0259 100644
--- a/libs/ardour/ardour/audio_port.h
+++ b/libs/ardour/ardour/audio_port.h
@@ -47,6 +47,7 @@ public:
 	}
 
 	AudioBuffer& get_audio_buffer (pframes_t nframes);
+	void set_buffer_size (pframes_t nframes);
 
 protected:
 	friend class PortManager;
diff --git a/libs/ardour/ardour/port.h b/libs/ardour/ardour/port.h
index 427a510d22..d2fb0ed03f 100644
--- a/libs/ardour/ardour/port.h
+++ b/libs/ardour/ardour/port.h
@@ -123,6 +123,7 @@ public:
 	virtual void flush_buffers (pframes_t /*nframes*/) {}
 	virtual void transport_stopped () {}
 	virtual void realtime_locate () {}
+	virtual void set_buffer_size (pframes_t) {}
 
 	bool physically_connected () const;
 	uint32_t externally_connected () const { return _externally_connected; }
diff --git a/libs/ardour/ardour/port_manager.h b/libs/ardour/ardour/port_manager.h
index 9a156c147e..46e6dc77ad 100644
--- a/libs/ardour/ardour/port_manager.h
+++ b/libs/ardour/ardour/port_manager.h
@@ -223,6 +223,8 @@ class LIBARDOUR_API PortManager
 	void fill_midi_port_info_locked ();
 
 	void filter_midi_ports (std::vector<std::string>&, MidiPortFlags, MidiPortFlags);
+
+	void set_port_buffer_sizes (pframes_t);
 };
 
 
diff --git a/libs/ardour/audio_port.cc b/libs/ardour/audio_port.cc
index 878f6c2625..6d0a90a187 100644
--- a/libs/ardour/audio_port.cc
+++ b/libs/ardour/audio_port.cc
@@ -29,6 +29,7 @@
 #include "ardour/audio_port.h"
 #include "ardour/data_type.h"
 #include "ardour/port_engine.h"
+#include "ardour/rc_configuration.h"
 
 using namespace ARDOUR;
 using namespace std;
@@ -39,19 +40,26 @@ using namespace std;
 AudioPort::AudioPort (const std::string& name, PortFlags flags)
 	: Port (name, DataType::AUDIO, flags)
 	, _buffer (new AudioBuffer (0))
+	, _data (0)
 {
 	assert (name.find_first_of (':') == string::npos);
-	cache_aligned_malloc ((void**) &_data, sizeof (Sample) * 8192);
 	_src.setup (_resampler_quality);
 	_src.set_rrfilt (10);
 }
 
 AudioPort::~AudioPort ()
 {
-	cache_aligned_free (_data);
+	if (_data) cache_aligned_free (_data);
 	delete _buffer;
 }
 
+void
+AudioPort::set_buffer_size (pframes_t nframes)
+{
+	if (_data) cache_aligned_free (_data);
+	cache_aligned_malloc ((void**) &_data, sizeof (Sample) * lrint (floor (nframes * Config->get_max_transport_speed())));
+}
+
 void
 AudioPort::cycle_start (pframes_t nframes)
 {
diff --git a/libs/ardour/audioengine.cc b/libs/ardour/audioengine.cc
index e6961af875..73e48f1e93 100644
--- a/libs/ardour/audioengine.cc
+++ b/libs/ardour/audioengine.cc
@@ -181,6 +181,8 @@ AudioEngine::sample_rate_change (pframes_t nframes)
 int
 AudioEngine::buffer_size_change (pframes_t bufsiz)
 {
+	set_port_buffer_sizes (bufsiz);
+
 	if (_session) {
 		_session->set_block_size (bufsiz);
 		last_monitor_check = 0;
diff --git a/libs/ardour/port.cc b/libs/ardour/port.cc
index 4caace07c0..03210baf80 100644
--- a/libs/ardour/port.cc
+++ b/libs/ardour/port.cc
@@ -26,13 +26,13 @@
 #include "pbd/compose.h"
 #include "pbd/error.h"
 #include "pbd/failed_constructor.h"
+#include "pbd/i18n.h"
 
 #include "ardour/audioengine.h"
 #include "ardour/debug.h"
 #include "ardour/port.h"
 #include "ardour/port_engine.h"
-
-#include "pbd/i18n.h"
+#include "ardour/rc_configuration.h"
 
 using namespace std;
 using namespace ARDOUR;
@@ -645,10 +645,11 @@ Port::set_state (const XMLNode& node, int)
 /*static*/ void
 Port::set_speed_ratio (double s) {
 	/* see VMResampler::set_rratio() for min/max range */
-	_speed_ratio = std::min (16.0, std::max (0.5, s));
+	_speed_ratio = std::min ((double) Config->get_max_transport_speed(), std::max (0.5, s));
 }
 
 /*static*/ void
-Port::set_cycle_samplecnt (pframes_t n) {
+Port::set_cycle_samplecnt (pframes_t n)
+{
 	_cycle_nframes = floor (n * _speed_ratio);
 }
diff --git a/libs/ardour/port_manager.cc b/libs/ardour/port_manager.cc
index 8d9f47cf84..75d93af320 100644
--- a/libs/ardour/port_manager.cc
+++ b/libs/ardour/port_manager.cc
@@ -420,12 +420,13 @@ PortManager::register_port (DataType dtype, const string& portname, bool input,
 			throw PortRegistrationFailure (string_compose ("unable to create port '%1': %2", portname, _("(unknown type)")));
 		}
 
+		newport->set_buffer_size (AudioEngine::instance()->samples_per_cycle());
+
 		RCUWriter<Ports> writer (ports);
 		boost::shared_ptr<Ports> ps = writer.get_copy ();
 		ps->insert (make_pair (make_port_name_relative (portname), newport));
 
 		/* writer goes out of scope, forces update */
-
 	}
 
 	catch (PortRegistrationFailure& err) {
@@ -1353,3 +1354,14 @@ PortManager::fill_midi_port_info_locked ()
 
 	midi_info_dirty = false;
 }
+
+void
+PortManager::set_port_buffer_sizes (pframes_t n)
+{
+
+	boost::shared_ptr<Ports> all = ports.reader();
+
+	for (Ports::iterator p = all->begin(); p != all->end(); ++p) {
+		p->second->set_buffer_size (n);
+	}
+}