diff --git a/libs/ardour/ardour/system_exec.h b/libs/ardour/ardour/system_exec.h
index ae865c7bff..010a076c01 100644
--- a/libs/ardour/ardour/system_exec.h
+++ b/libs/ardour/ardour/system_exec.h
@@ -35,8 +35,8 @@ public:
 	SystemExec (std::string c, const std::map<char, std::string> subs);
 	~SystemExec ();
 
-	int start (int stderr_mode = 1) {
-		return PBD::SystemExec::start(stderr_mode, _vfork_exec_wrapper);
+	int start (StdErrMode stderr_mode = IgnoreAndClose) {
+		return PBD::SystemExec::start (stderr_mode, _vfork_exec_wrapper);
 	}
 
 private:
diff --git a/libs/ardour/export_graph_builder.cc b/libs/ardour/export_graph_builder.cc
index 2fd1df2e89..5afb5c1e7d 100644
--- a/libs/ardour/export_graph_builder.cc
+++ b/libs/ardour/export_graph_builder.cc
@@ -383,7 +383,7 @@ ExportGraphBuilder::Encoder::init_writer (boost::shared_ptr<AudioGrapher::CmdPip
 	 * SystemExec is deleted when writer is destroyed */
 	ARDOUR::SystemExec* exec = new ARDOUR::SystemExec (ffmpeg_exe, argp);
 	PBD::info << "Encode command: { " << exec->to_s () << "}" << endmsg;
-	if (exec->start(0)) {
+	if (exec->start ()) {
 		throw ExportFailed ("External encoder (ffmpeg) cannot be started.");
 	}
 	writer.reset (new AudioGrapher::CmdPipeWriter<T> (exec, writer_filename));
diff --git a/libs/ardour/export_handler.cc b/libs/ardour/export_handler.cc
index cd3d61731d..c39d630d69 100644
--- a/libs/ardour/export_handler.cc
+++ b/libs/ardour/export_handler.cc
@@ -422,7 +422,7 @@ ExportHandler::finish_timespan ()
 			ARDOUR::SystemExec *se = new ARDOUR::SystemExec(fmt->command(), subs);
 			info << "Post-export command line : {" << se->to_s () << "}" << endmsg;
 			se->ReadStdout.connect_same_thread(command_connection, boost::bind(&ExportHandler::command_output, this, _1, _2));
-			int ret = se->start (2);
+			int ret = se->start (SystemExec::MergeWithStdin);
 			if (ret == 0) {
 				// successfully started
 				while (se->is_running ()) {
diff --git a/libs/ardour/vst_info_file.cc b/libs/ardour/vst_info_file.cc
index d6d946dee6..189288ce15 100644
--- a/libs/ardour/vst_info_file.cc
+++ b/libs/ardour/vst_info_file.cc
@@ -998,7 +998,7 @@ vstfx_get_info (const char* dllpath, enum ARDOUR::PluginType type, enum VSTScanM
 		ARDOUR::SystemExec scanner (scanner_bin_path, argp);
 		PBD::ScopedConnectionList cons;
 		scanner.ReadStdout.connect_same_thread (cons, boost::bind (&parse_scanner_output, _1 ,_2));
-		if (scanner.start (2 /* send stderr&stdout via signal */)) {
+		if (scanner.start (ARDOUR::SystemExec::MergeWithStdin)) {
 			PBD::error << string_compose (_("Cannot launch VST scanner app '%1': %2"), scanner_bin_path, strerror (errno)) << endmsg;
 			close_error_log ();
 			return infos;
diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 1355197522..00c6940d7c 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -2831,7 +2831,7 @@ AlsaDeviceReservation::acquire_device (const char* device_name)
 	_device_reservation->ReadStdout.connect_same_thread (_reservation_connection, boost::bind (&AlsaDeviceReservation::reservation_stdout, this, _1 ,_2));
 	_device_reservation->Terminated.connect_same_thread (_reservation_connection, boost::bind (&AlsaDeviceReservation::release_device, this));
 
-	if (_device_reservation->start(0)) {
+	if (_device_reservation->start (SystemExec::ShareWithParent)) {
 		PBD::warning << _("AlsaAudioBackend: Device Request failed.") << endmsg;
 		release_device();
 		return false;
diff --git a/libs/pbd/pbd/system_exec.h b/libs/pbd/pbd/system_exec.h
index 1e36c3df9f..a567e3b032 100644
--- a/libs/pbd/pbd/system_exec.h
+++ b/libs/pbd/pbd/system_exec.h
@@ -122,6 +122,12 @@ class LIBPBD_API SystemExec
 
 		std::string to_s() const;
 
+		enum StdErrMode {
+			ShareWithParent = 0,
+			IgnoreAndClose  = 1,
+			MergeWithStdin  = 2
+		};
+
 		/** fork and execute the given program
 		 *
 		 * @param stderr_mode select what to do with program's standard error
@@ -133,7 +139,7 @@ class LIBPBD_API SystemExec
 		 * @return If the process is already running or was launched successfully
 		 * the function returns zero (0). A negative number indicates an error.
 		 */
-		int start (int stderr_mode, const char *_vfork_exec_wrapper);
+		int start (StdErrMode, const char *_vfork_exec_wrapper);
 		/** kill running child-process
 		 *
 		 * if a child process exists trt to shut it down by closing its STDIN.
diff --git a/libs/pbd/system_exec.cc b/libs/pbd/system_exec.cc
index b7a7f87123..23f808a0c3 100644
--- a/libs/pbd/system_exec.cc
+++ b/libs/pbd/system_exec.cc
@@ -529,7 +529,7 @@ SystemExec::is_running ()
 }
 
 int
-SystemExec::start (int stderr_mode, const char * /*vfork_exec_wrapper*/)
+SystemExec::start (StdErrMode stderr_mode, const char * /*vfork_exec_wrapper*/)
 {
 	char* working_dir = 0;
 
@@ -541,10 +541,10 @@ SystemExec::start (int stderr_mode, const char * /*vfork_exec_wrapper*/)
 	create_pipe(stdinP, true);
 	create_pipe(stdoutP, false);
 
-	if (stderr_mode == 2) {
+	if (stderr_mode == MergeWithStdin) {
 	/* merge stout & stderr */
 		DuplicateHandle(GetCurrentProcess(), stdoutP[1], GetCurrentProcess(), &stderrP[1], 0, TRUE, DUPLICATE_SAME_ACCESS);
-	} else if (stderr_mode == 1) {
+	} else if (stderr_mode == IgnoreAndClose) {
 		//TODO read/flush this pipe or close it...
 		create_pipe(stderrP, false);
 	} else {
@@ -807,7 +807,7 @@ SystemExec::is_running ()
 }
 
 int
-SystemExec::start (int stderr_mode, const char *vfork_exec_wrapper)
+SystemExec::start (StdErrMode stderr_mode, const char *vfork_exec_wrapper)
 {
 	if (is_running ()) {
 		return 0;
@@ -889,12 +889,12 @@ SystemExec::start (int stderr_mode, const char *vfork_exec_wrapper)
 		::dup2 (pout[1], STDOUT_FILENO);
 	}
 
-	if (stderr_mode == 2) {
+	if (stderr_mode == MergeWithStdin) {
 		/* merge STDERR into output */
 		if (pout[1] != STDERR_FILENO) {
 			::dup2(pout[1], STDERR_FILENO);
 		}
-	} else if (stderr_mode == 1) {
+	} else if (stderr_mode == IgnoreAndClose) {
 		/* ignore STDERR */
 		::close(STDERR_FILENO);
 	} else {