In second language (L2) research and testing, measures of oral fluency are used as diagnostics for proficiency. However, fluency is also determined by personality or speaking style, raising the question to what extent L2 fluency measures are valid indicators of L2 proficiency. In this study, we obtained a measure of L2 (Dutch) proficiency (vocabulary knowledge), L2 fluency measures, and fluency measures that were corrected for first language behavior from the same group of Turkish and English native speakers (N = 51). For most measures of fluency, except for silent pause duration, both the corrected and the uncorrected measures significantly predicted L2 proficiency. For syllable duration, the corrected measure was a stronger predictor of L2 proficiency than was the uncorrected measure. We conclude that for L2 research purposes, as well as for some types of L2 testing, it is useful to obtain corrected measures of syllable duration to measure L2-specific fluency.Imagine two immigrants who have learned to speak Dutch as their second language (L2), let us say Oscar and Mark. Both have acquired Dutch after adolescence and find themselves at an intermediate level of oral proficiency. However, they happen to differ in their level of speaking fluency: Compared to other speakers, Mark seems to use many filled pauses ("uhms") in his L2 speech, whereas Oscar only uses a few filled pauses. Should we therefore conclude that Oscar and Mark operate at different levels of oral proficiency, evidenced by the different levels of speaking fluency? Now imagine that we also know how they speak in their native (first) language (L1). It turns out that Oscar rarely uses a filled pause in his L1 speech, whereas Mark exhibits many filled pauses in his L1. Can we still conclude that