The paper is dedicated to a self-assessment approach as a means of addressing fossilized errors in L2 speaking within the professional communication framework. The phenomenon of fossilization manifests in L2 spoken and written texts on phonological, lexical and grammatical level. Addressing the issue of fossilization has to deal with creating a perfect fluency/accuracy balance, increase of fluency in L2 classroom settings inevitably results in fossilized errors in learners as it compromises their accuracy on a permanent basis. In this respect it is interesting to look into common practices of addressing fossilized errors in advanced L2 classroom. This work is a case study of an attempt to address individual fossilized errors in L2 C1-level students at university level. The paper argues that self-assessment as a means of developing metacognitive awareness and consciousness of advanced L2 learners is a valid tool for eliminating fossilized errors in the long run. We present the results of case study that took place at RUDN university in 2018 within 3 months. During this period a group of advanced L2 learners were asked to record their spontaneous pair interactions, transcribe the conversations and correct their own mistakes. The corrected transcripts were submitted to the L2 instructor for further evaluation and assessment. Small corpora of error-tagged conversations were created for each individual student. Then the instructor created a report on individual mistakes and errors on monthly basis. Persistent, fossilized errors were registered for each individual case and measured at the beginning for the pedagogical experiment and at its end. The paper presents our findings, positive dynamics and overall pedagogical value of establishing correlation between students' previous knowledge and self-assessment.