In recent years, there has been growing interest in research on sustainability in software engineering. Despite active research in this area, there is still a lack of understanding of how sustainability is perceived by software professionals. To understand how software sustainability is currently dealt with in practice, we performed an interview study with 10 software project team leads from nine companies in Austria. Our study shows that practitioners regard software sustainability as important but are technically minded with respect to sustainability. Organizational and economic issues are addressed, but environmental considerations are missing. The perceived influence of various project factors on sustainability is partly diverse, suggesting that the meaning of sustainability needs to be refined for the specific project and application context.