This study examines the role of listeners' native language (L1) background in judgments of comprehensibility (ease of understanding) for speakers from same and different L1 backgrounds, to determine the extent of a shared second language (L2) comprehensibility benefit. Forty L2 English speakers from Mandarin, French, Hindi, and English backgrounds (10 per group) listened to speech samples from 30 L2 English speakers from Mandarin, French, and Hindi backgrounds (10 per group). Listeners first evaluated each speaker's comprehensibility and provided verbal reports indicating their reasons for each rating. To estimate pronunciation influences on comprehensibility, listeners then rated each speaker for four speech measures (segmental and word stress errors, intonation, speech rate). Results revealed that different speech measures were associated with comprehensibility ratings for different listener-speaker groups, and that a match in L1 background accounted for additional unique variance in comprehensibility ratings, but only for the Mandarin listeners and speakers. Verbal reports indicated that listeners more often considered L1 a benefit when rating speakers from their own L1 and a detriment when evaluating speakers from a different L1. Findings overall point to small effects of shared L1 background on comprehensibility, suggesting alternative priorities for teaching and researching comprehensible L2 speech.