The aim of this study is to explore (1) what written corrective feedback strategies are used to address students' written mistakes, particularly grammatical mistakes, and (2) what common grammatical mistakes are made by students at Swedish upper secondary schools. Eight teachers in central Sweden were asked to participate in this study, and two decided to take part. The teachers then had to gather confirmation from their students to submit texts produced by students on which the teachers had given written corrective feedback. The student texts, along with the written corrective feedback, were analysed and categorised using descriptive categorical data. The result shows that the corrective feedback strategy used is based on what the teacher prefers. In this study, one seemed to prefer direct corrective feedback and the other metalinguistic feedback. Both teachers only used unfocused direct corrective feedback on the grammatical mistakes, resulting in most, if not all, grammatical mistakes receiving corrective feedback. Furthermore, the most common grammatical mistakes marked in the texts were not fully in line with previous research, as only one aspect was common: subject-verb agreement. The other two most common ones were lack of commas and capitalisation, which would need more research to understand why.