diff --git a/libs/ardour/port_engine_shared.cc b/libs/ardour/port_engine_shared.cc
index cd9c4b3da5..5aae77f2a4 100644
--- a/libs/ardour/port_engine_shared.cc
+++ b/libs/ardour/port_engine_shared.cc
@@ -81,7 +81,7 @@ BackendPort::connect (BackendPortHandle port, BackendPortHandle self)
 			<< " (" << name () << ") -> (" << port->name () << ")"
 			<< endmsg;
 #endif
-		return -1;
+		return 0;
 	}
 
 	store_connection (port);
diff --git a/libs/backends/jack/jack_portengine.cc b/libs/backends/jack/jack_portengine.cc
index bc78aa95b9..942da6b26b 100644
--- a/libs/backends/jack/jack_portengine.cc
+++ b/libs/backends/jack/jack_portengine.cc
@@ -617,7 +617,11 @@ int
 JACKAudioBackend::connect (PortHandle port, const std::string& other)
 {
 	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);
-	return jack_connect (_priv_jack, jack_port_name (boost::dynamic_pointer_cast<JackPort>(port)->jack_ptr), other.c_str());
+	int r = jack_connect (_priv_jack, jack_port_name (boost::dynamic_pointer_cast<JackPort>(port)->jack_ptr), other.c_str());
+	if (r == 0 || r == EEXIST) {
+		return 0;
+	}
+	return r;
 }
 int
 JACKAudioBackend::connect (const std::string& src, const std::string& dst)
@@ -625,6 +629,9 @@ JACKAudioBackend::connect (const std::string& src, const std::string& dst)
 	GET_PRIVATE_JACK_POINTER_RET (_priv_jack, -1);
 
 	int r = jack_connect (_priv_jack, src.c_str(), dst.c_str());
+	if (r == 0 || r == EEXIST) {
+		return 0;
+	}
 	return r;
 }