diff --git a/util/modbus/modbus.go b/util/modbus/modbus.go
index 2283faa1f..86aa504f5 100644
--- a/util/modbus/modbus.go
+++ b/util/modbus/modbus.go
@@ -88,6 +88,7 @@ func unregisterConnection(key string) {
 		return
 	}
 
+	conn.Close()
 	delete(connections, key)
 }