This study compares the quality of postediting performed by subject-matter experts as opposed to professional translators. A total of 10 professional translators and 10 engineers postedited a 482-word technical text pre-translated from English into Turkish using data-based machine translation system, Google Translate. The findings suggest that, for this particular task (technical translation), translators' and engineers' postediting quality is similar as far as the categories of mistranslation, accuracy, and consistency are concerned. Engineers performed significantly better than translators only in the terminology category. In the language category, translators made significantly fewer (minor) errors than engineers. The qualitative data analysis revealed that, for this particular task, a degree in translation does not directly correlate with postediting quality, unless it is combined with subject-matter knowledge and professional experience in translation. Finally, the present study indicates that - both for the engineers and the professional translators - expertise and experience in the subject matter are important factors determining postediting quality.