Developing comprehensible speech is an important goal for L2 learners. At present, there is clear evidence indicating that pronunciation instruction can help develop comprehensibility compared to no instruction at all (see Thomson & Derwing, 2015, for a review). However, it is unclear whether rapid improvements can be obtained through explicit pronunciation instruction. This study investigated the effects of explicit and nonexplicit instruction in the development of comprehensible speech in ESL learners. Three groups (n = 12) received about four hours of pronunciation instruction over three weeks using the same teaching sequence. Groups differed in the type of explicit instruction received: two experimental groups received explicit instruction either on suprasegmental features or four vowel sounds. The same content was presented to the third group without explicit instruction. Speech samples collected from all L2 learners before and after treatment revealed an effect of explicit instruction on comprehensibility: the group instructed in suprasegmentals was rated as more comprehensible. No significant improvement was seen in the nonexplicit group. These results suggest that focusing on suprasegmental aspects seems to be most effective for comprehensibility when time is limited, and argue for a major role for explicit phonetic instruction in developing enhanced comprehensibility (e.g., Derwing, Munro, & Wiebe, 1998; Munro, 1995).