Permissions for using single workflow

Hello,
I am new to Mayan and am having some difficulties with rights management.

I have a workflow which should be able to be executed by a role. If I check the authorization “Perform transition of instances” in the flow, the users of the role get an error and cannot open the page.
Only when I assign the permission in the role can the user access it. However, the user can then change and execute any flow.

I may be missing something. How can I ensure that the user can only execute the specific workflow?