Despite its success in the software industry, Software-as-a-Service (SaaS) still struggles with fulfilling customer expectations regarding service quality. To contain customer churn rates to low levels, SaaS providers have to address their service quality weak spots and find out which factors are crucial for continued SaaS usage. Drawing on previous service quality literature, we develop a Zone-of-Tolerance (ZOT)-based SaaS-QUAL scale and validate it in a model of IS continuance based on two empirical surveys of SaaS using firms. By doing this, we examine the importance of SaaS service quality factors for shaping customer satisfaction and SaaS continuance intentions. Furthermore, we provide insights into what service factors effectively meet or miss SaaS customer expectations. As a practical contribution, we develop and apply a SaaS-QUAL scale that can be used as a diagnostic tool by SaaS providers and users alike. For researchers, we enrich existing research models on IS continuance by integrating a more fine-grained conceptualization of service quality confirmation that provides stronger explanatory power than in previous models.