diff --git a/libs/ardour/ardour/diskstream.h b/libs/ardour/ardour/diskstream.h
index d6f3b739e9..e135d1319b 100644
--- a/libs/ardour/ardour/diskstream.h
+++ b/libs/ardour/ardour/diskstream.h
@@ -131,7 +131,7 @@ class Diskstream : public SessionObject, public boost::noncopyable
 	/* Stateful */
 	virtual XMLNode& get_state(void) = 0;
 	virtual int      set_state(const XMLNode&, int version) = 0;
-	
+
 	virtual void monitor_input (bool) {}
 
 	nframes_t    capture_offset() const { return _capture_offset; }
@@ -246,6 +246,9 @@ class Diskstream : public SessionObject, public boost::noncopyable
 	virtual void setup_destructive_playlist () {}
 	virtual void use_destructive_playlist () {}
 
+	void calculate_record_range(OverlapType ot, sframes_t transport_frame, nframes_t nframes,
+			nframes_t& rec_nframes, nframes_t& rec_offset);
+
 	static nframes_t disk_io_chunk_frames;
 	std::vector<CaptureInfo*>  capture_info;
 	Glib::Mutex           capture_info_lock;
diff --git a/libs/ardour/audio_diskstream.cc b/libs/ardour/audio_diskstream.cc
index 4f631c50cb..599e5ea1f9 100644
--- a/libs/ardour/audio_diskstream.cc
+++ b/libs/ardour/audio_diskstream.cc
@@ -470,54 +470,14 @@ AudioDiskstream::process (nframes_t transport_frame, nframes_t nframes, bool can
 	}
 
 	if (nominally_recording || (_session.get_record_enabled() && _session.config.get_punch_in())) {
-		OverlapType ot;
-
 		// Safeguard against situations where process() goes haywire when autopunching and last_recordable_frame < first_recordable_frame
 		if (last_recordable_frame < first_recordable_frame) {
 			last_recordable_frame = max_frames;
 		}
 
-		ot = coverage (first_recordable_frame, last_recordable_frame, transport_frame, transport_frame + nframes);
+		OverlapType ot = coverage (first_recordable_frame, last_recordable_frame, transport_frame, transport_frame + nframes);
 
-		switch (ot) {
-		case OverlapNone:
-			rec_nframes = 0;
-			break;
-
-		case OverlapInternal:
-		/*     ----------    recrange
-                         |---|       transrange
-		*/
-			rec_nframes = nframes;
-			rec_offset = 0;
-			break;
-
-		case OverlapStart:
-			/*    |--------|    recrange
-                            -----|          transrange
-			*/
-			rec_nframes = transport_frame + nframes - first_recordable_frame;
-			if (rec_nframes) {
-				rec_offset = first_recordable_frame - transport_frame;
-			}
-			break;
-
-		case OverlapEnd:
-			/*    |--------|    recrange
-                                 |--------  transrange
-			*/
-			rec_nframes = last_recordable_frame - transport_frame;
-			rec_offset = 0;
-			break;
-
-		case OverlapExternal:
-			/*    |--------|    recrange
-                            --------------  transrange
-			*/
-			rec_nframes = last_recordable_frame - first_recordable_frame;
-			rec_offset = first_recordable_frame - transport_frame;
-			break;
-		}
+		calculate_record_range(ot, transport_frame, nframes, rec_nframes, rec_offset);
 
 		if (rec_nframes && !was_recording) {
 			capture_captured = 0;
diff --git a/libs/ardour/diskstream.cc b/libs/ardour/diskstream.cc
index 0b4c98eaa3..aaeb15a995 100644
--- a/libs/ardour/diskstream.cc
+++ b/libs/ardour/diskstream.cc
@@ -594,3 +594,48 @@ Diskstream::route_going_away ()
 {
 	_io.reset ();
 }
+
+void
+Diskstream::calculate_record_range(OverlapType ot, sframes_t transport_frame, nframes_t nframes,
+		nframes_t& rec_nframes, nframes_t& rec_offset)
+{
+	switch (ot) {
+	case OverlapNone:
+		rec_nframes = 0;
+		break;
+
+	case OverlapInternal:
+		/*     ----------    recrange
+		         |---|       transrange
+		*/
+		rec_nframes = nframes;
+		rec_offset = 0;
+		break;
+
+	case OverlapStart:
+		/*    |--------|    recrange
+	        -----|          transrange
+		*/
+		rec_nframes = transport_frame + nframes - first_recordable_frame;
+		if (rec_nframes) {
+			rec_offset = first_recordable_frame - transport_frame;
+		}
+		break;
+
+	case OverlapEnd:
+		/*    |--------|    recrange
+		         |--------  transrange
+		*/
+		rec_nframes = last_recordable_frame - transport_frame;
+		rec_offset = 0;
+		break;
+
+	case OverlapExternal:
+		/*    |--------|    recrange
+		    --------------  transrange
+		*/
+		rec_nframes = last_recordable_frame - first_recordable_frame;
+		rec_offset = first_recordable_frame - transport_frame;
+		break;
+	}
+}
diff --git a/libs/ardour/midi_diskstream.cc b/libs/ardour/midi_diskstream.cc
index 8172bd9d66..12d39426d8 100644
--- a/libs/ardour/midi_diskstream.cc
+++ b/libs/ardour/midi_diskstream.cc
@@ -528,49 +528,9 @@ MidiDiskstream::process (nframes_t transport_frame, nframes_t nframes, bool can_
 	adjust_capture_position = 0;
 
 	if (nominally_recording || (_session.get_record_enabled() && _session.config.get_punch_in())) {
-		OverlapType ot;
+		OverlapType ot = coverage (first_recordable_frame, last_recordable_frame, transport_frame, transport_frame + nframes);
 
-		ot = coverage (first_recordable_frame, last_recordable_frame, transport_frame, transport_frame + nframes);
-
-		switch (ot) {
-			case OverlapNone:
-				rec_nframes = 0;
-				break;
-
-			case OverlapInternal:
-				/*     ----------    recrange
-					   |---|       transrange
-					   */
-				rec_nframes = nframes;
-				rec_offset = 0;
-				break;
-
-			case OverlapStart:
-				/*    |--------|    recrange
-					  -----|          transrange
-					  */
-				rec_nframes = transport_frame + nframes - first_recordable_frame;
-				if (rec_nframes) {
-					rec_offset = first_recordable_frame - transport_frame;
-				}
-				break;
-
-			case OverlapEnd:
-				/*    |--------|    recrange
-					  |--------  transrange
-					  */
-				rec_nframes = last_recordable_frame - transport_frame;
-				rec_offset = 0;
-				break;
-
-			case OverlapExternal:
-				/*    |--------|    recrange
-					  --------------  transrange
-					  */
-				rec_nframes = last_recordable_frame - last_recordable_frame;
-				rec_offset = first_recordable_frame - transport_frame;
-				break;
-		}
+		calculate_record_range(ot, transport_frame, nframes, rec_nframes, rec_offset);
 
 		if (rec_nframes && !was_recording) {
 			capture_captured = 0;