The literature on English for Specific Purposes (ESP) has largely ignored one of its most distinctive features: many ESP teachers have to teach subject-specific texts from areas outside their primary areas of expertise. This paper addresses this issue by investigating the teaching practices and cognitions of three teachers of maritime English in a college in China, and in particular how they respond to unpredicted situations in-class where their subject knowledge is limited--what we call "In-class Subject Knowledge Dilemma" (ISKD) situations. In six lessons, we identified five episodes where the teacher had to deal with an unpredicted issue related to subject knowledge. The strategies that the teachers used when dealing with these episodes can be described in terms of avoidance or risk taking. The teachers believed that the occurrence of such unpredicted problems reflected poorly on their competence as teachers but that the strategies they adopted meant that the lesson proceeded smoothly and allowed them to maintain their students' respect as experts in the field. (Contains 3 tables.)