diff --git a/libs/ardour/ardour/processor.h b/libs/ardour/ardour/processor.h
index c639f25fb1..2b5402df24 100644
--- a/libs/ardour/ardour/processor.h
+++ b/libs/ardour/ardour/processor.h
@@ -45,6 +45,18 @@ namespace ARDOUR {
 class Location;
 class Session;
 
+class LIBARDOUR_API ProcessorException: public std::exception
+{
+public:
+	explicit ProcessorException (const std::string msg) : _message(msg) {}
+	virtual ~ProcessorException () throw() {}
+
+	virtual const char* what() const throw() { return _message.c_str(); }
+
+private:
+	std::string _message;
+};
+
 /** A mixer strip element - plugin, send, meter, etc */
 class LIBARDOUR_API Processor : public SessionObject, public Automatable, public Latent
 {
diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 94ec405757..ddc7eab165 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -461,6 +461,9 @@ Session::Session (AudioEngine &eng,
 			case -6:
 				throw SessionException (string_compose (_("Cannot initialize session/engine: %1"), _("Audio/MIDI Engine is not running or sample-rate mismatches.")));
 				break;
+			case -8:
+				throw SessionException (string_compose (_("Cannot initialize session/engine: %1"), _("Required Plugin/Processor is missing.")));
+				break;
 			default:
 				throw SessionException (string_compose (_("Cannot initialize session/engine: %1"), _("Unexpected exception during session setup, possibly invalid audio/midi engine parameters. Please see stdout/stderr for details")));
 				break;
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index ee2189d725..2692e9d3eb 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -381,6 +381,9 @@ Session::post_engine_init ()
 	} catch (AudioEngine::PortRegistrationFailure& err) {
 		error << err.what() << endmsg;
 		return -5;
+	} catch (ProcessorException const & e) {
+		error << e.what() << endmsg;
+		return -8;
 	} catch (std::exception const & e) {
 		error << _("Unexpected exception during session setup: ") << e.what() << endmsg;
 		return -6;