The acquisition of a second language (L2) may be challenging in adulthood, as the phonological system of the native language (L1) can sometimes limit the perception of phonological contrasts in L2. The present study aimed to (a) examine the influence of an L1 (Hebrew) that lacks a phonemic contrast for vowel length on the ability to discriminate between short and long vowels in L2 (Arabic); and (b) assess the effect of a short training on the participants' discrimination performance. A total of 60 participants, 20 native Arabic speakers and 40 native Hebrew speakers, were tested using the ABX procedure in two sessions that were 10Â days apart. A single training session was provided for half of the Hebrew speakers (nÂ =Â 20) approximately 2-3Â days after the first (pretraining) testing session. The results indicated that the trained Hebrew participants' discrimination levels (measured by accuracy and reaction times) were above chance level but were nevertheless lower in comparison to the Arabic speakers. However, a short training session was sufficient to yield a nativelike performance that generalized to untrained nonwords. These findings support the theoretical models that predict a reserved ability to acquire new phonetic/phonological cues in L2 and have important practical implications for the process of learning a new phonological system in adulthood.