The goal of English pronunciation teaching has shifted from native-likeness to intelligibility. Especially in EFL contexts, pushing learners to sound like L1 speakers is difficult to justify, whereas becoming intelligible is an easily justifiable, practical learning goal. However, EFL teachers often emphasize the sounds that are typically challenging for their learners, even though all sounds are not equally important for intelligibility. The present study is focussed on the extent to which segmental deviations can compromise intelligibility. Speech samples were elicited from teenaged L1 Finnish learners of English, demonstrating segmental deviations typical of the target group. To evaluate the gravity of segmental deviation, an intelligibility test was arranged with L1 English listeners. Results suggest that the sounds under investigation can be ranked into groups based on how crucial they are for intelligibility. The ranking can help EFL teachers to prioritize the critical sounds over those that are unlikely to compromise intelligibility.