Dyslexia is hard to diagnose in a second language. Poor performance on a test of reading may be caused by poor language proficiency in the second language or by limited schooling rather than by poor reading ability per se. This confound was supported in a study of 88 adult second language learners and 65 native language speakers. The incidence of dyslexia in the second language learners varied widely depending on the measure of reading. In order to reduce language and schooling confounds, a dynamic test of acquisition of basic decoding ability was developed. In the dynamic test, participants are taught three novel letters and to synthesise the letter sounds into new words. Results from the study indicated that the dynamic test provided results in accordance with the current IDA definition of dyslexia, while significantly reducing the influence second language vocabulary and amount of schooling. With the dynamic measure, the same cut-off point between dyslexic and non-dyslexic performance appeared valid in both native language speakers and second language learners.