The necessity to embrace frequent and hard to predict changes in the businesses of enterprises has led to the need for continuous information systems engineering in order to support the enterprises with appropriate information services. Systems engineering prescribes a particular process of systems development from well defined requirements to the verified and validated resulting system. This process, even applied continuously, only partly can be followed in information systems engineering. First, the information system is a socio-technical system, therefore it is impossible to fully engineer it. Second, frequent changes in information system can rapidly cause its deviation from the initial design even up to losing its systemic properties to some extent. The paper claims that systemic properties of information systems should be checked during continuous information systems engineering to support viability of enterprises. The Viable Systems Model and consideration of ecosystemic dependency are proposed as means for assuring systemic soundness of engineered information systems.