diff --git a/v2c/integrationpluginv2c.cpp b/v2c/integrationpluginv2c.cpp
index 0c428e5..fba02de 100644
--- a/v2c/integrationpluginv2c.cpp
+++ b/v2c/integrationpluginv2c.cpp
@@ -68,13 +68,23 @@ void IntegrationPluginV2c::setupThing(ThingSetupInfo *info)
     const quint16 port    = static_cast<quint16>(thing->paramValue(trydanThingPortParamTypeId).toUInt());
     const quint16 slaveId = 1; // V2C Trydan always uses unit ID 1
 
-    TrydanModbusTcpMaster *master = new TrydanModbusTcpMaster(
-        monitor->networkDeviceInfo().address(), port, slaveId, thing);
+    // Prefer the monitor's cached address (ARP/mDNS already resolved) but fall back
+    // to the stored address param.  The monitor has a null address at first
+    // registerMonitor() when the device was added by IP (createMethod "user") or when
+    // nymead restarts before the monitor's ARP scan completes — connecting to a null
+    // QHostAddress would produce "device ':502'" and fail immediately.
+    QHostAddress address = monitor->networkDeviceInfo().address();
+    if (address.isNull())
+        address = QHostAddress(thing->paramValue(trydanThingAddressParamTypeId).toString());
 
-    // Update target IP if the device gets a new DHCP lease.
+    TrydanModbusTcpMaster *master = new TrydanModbusTcpMaster(address, port, slaveId, thing);
+
+    // Update target IP when DHCP renews.  Guard against transient null info that
+    // the monitor can emit during its own internal refresh cycles.
     connect(monitor, &NetworkDeviceMonitor::networkDeviceInfoChanged,
             master, [master](const NetworkDeviceInfo &info) {
-        master->setHostAddress(info.address());
+        if (!info.address().isNull())
+            master->setHostAddress(info.address());
     });
 
     // Abort the setup if the info object is destroyed before we finish.