Recently, business processes started to become more collaborative by nature. Prominent examples of collaborative processes can be found in domains such as supply chain management, e-commerce, and in the realm of online multisided platforms. These types of collaborations are characterized by the fact that a collaborator's subprocess execution is usually beyond the control of other collaborators. This property leads to the occurrence of uncertainty in the processes. If uncertainty is present in a collaboration, then trust is needed. This article proposes a method to identify uncertainty within collaborative business processes and to add a trust layer to their modeled representation. The trust layer allows process collaborators to make implicit uncertainties explicit within a process model. The proposed methodology is not meant to be applied not only in a postprocessing fashion, but also for the specification of new collaborative processes with trust-aware design principles.