We examined whether observers' language proficiencies affected their abilities to detect native and non‐native speakers' deception. Native and non‐native English speakers were videotaped as they either lied or told the truth about having cheated on a test. A total of 284 laypersons—who were either native or non‐native English speakers themselves—viewed these videos and indicated whether they believed that the speakers were being truthful or deceptive. Observers were more accurate when judging native speakers than when judging non‐native speakers, suggesting that perceptual fluency aided deception detection. Although there was no effect of observers' language proficiencies on discrimination, their belief that interviewees were telling the truth increased with proficiency. On the whole, these findings suggest that non‐native speakers may be at greater risk of being incorrectly classified in forensic contexts.Copyright © 2017 John Wiley & Sons, Ltd.