diff --git a/Machines/Commodore/1540/Commodore1540.hpp b/Machines/Commodore/1540/Commodore1540.hpp
index 378ecb35c..7e57eb2ff 100644
--- a/Machines/Commodore/1540/Commodore1540.hpp
+++ b/Machines/Commodore/1540/Commodore1540.hpp
@@ -52,7 +52,7 @@ class SerialPortVIA: public MOS::MOS6522<SerialPortVIA>, public MOS::MOS6522IRQD
 				case ::Commodore::Serial::Line::Clock:		_portB = (_portB & ~0x04) | (value ? 0 : 0x04);		break;
 				case ::Commodore::Serial::Line::Attention:
 					_portB = (_portB & ~0x80) | (value ? 0 : 0x80);
-					set_control_line_input(Port::B, Line::Two, value);
+					set_control_line_input(Port::B, Line::Two, !value);	// from active low to active high
 				break;
 			}
 		}
diff --git a/Machines/Commodore/SerialBus.cpp b/Machines/Commodore/SerialBus.cpp
index c4e3a3f2c..be76aaef5 100644
--- a/Machines/Commodore/SerialBus.cpp
+++ b/Machines/Commodore/SerialBus.cpp
@@ -14,7 +14,13 @@ void Bus::add_port(std::shared_ptr<Port> port)
 {
 	_ports.push_back(port);
 	for(int line = (int)ServiceRequest; line <= (int)Reset; line++)
+	{
+		// the addition of a new device may change the line output...
 		set_line_output_did_change((Line)line);
+
+		// ... but the new device will need to be told the current state regardless
+		port->set_input((Line)line, _line_values[line]);
+	}
 }
 
 void Bus::set_line_output_did_change(Line line)