diff --git a/libs/ardour/ltc_slave.cc b/libs/ardour/ltc_slave.cc
index b1b4f71734..4f47b904bd 100644
--- a/libs/ardour/ltc_slave.cc
+++ b/libs/ardour/ltc_slave.cc
@@ -510,7 +510,7 @@ LTC_TransportMaster::speed_and_position (double& speed, samplepos_t& pos, sample
 }
 
 void
-LTC_TransportMaster::pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+LTC_TransportMaster::pre_process (ARDOUR::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
 {
 	Sample* in = (Sample*) AudioEngine::instance()->port_engine().get_buffer (_port->port_handle(), nframes);
 	sampleoffset_t skip = now - (monotonic_cnt + nframes);
diff --git a/libs/ardour/midi_clock_slave.cc b/libs/ardour/midi_clock_slave.cc
index 93ca9059ef..04fa259519 100644
--- a/libs/ardour/midi_clock_slave.cc
+++ b/libs/ardour/midi_clock_slave.cc
@@ -114,7 +114,7 @@ MIDIClock_TransportMaster::speed_and_position (double& speed, samplepos_t& pos,
 }
 
 void
-MIDIClock_TransportMaster::pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+MIDIClock_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
 {
 	/* Read and parse incoming MIDI */
 
diff --git a/libs/ardour/mtc_slave.cc b/libs/ardour/mtc_slave.cc
index 409fb9da69..a2b73ba2f4 100644
--- a/libs/ardour/mtc_slave.cc
+++ b/libs/ardour/mtc_slave.cc
@@ -130,7 +130,7 @@ MTC_TransportMaster::set_session (Session *s)
 }
 
 void
-MTC_TransportMaster::pre_process (pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
+MTC_TransportMaster::pre_process (MIDI::pframes_t nframes, samplepos_t now, boost::optional<samplepos_t> session_pos)
 {
 	/* Read and parse incoming MIDI */