The Software Engineering Institute's Softwares Process Maturity Model was developed to provide a basis for assessing an organization's ability to perform software engineering activities. It also provides a guide for improving an organization's software engineering capability. The maturity model was designed on the basis of concepts associated with developing new, large, complex systems. This has led to difficulties in applying the model to organizations involved entirely in software maintenance. The author addresses the tailoring issues encountered in applying the software maturity model to a large maintenance organization at Paramax Space Systems Operation. It is concluded that the issues that arise when the Capability Maturity Model is applied to a software sustaining engineering organization are significant but do not prohibit the use of the model as a guide for software process improvement. Issues mainly arise with the treatment requirements and differences in project management needs. The primary tailoring issues are ones of wording as opposed to applicability to maintenance activities. >