JVMS 4.10.1.4 introduces the idea that some verification types take up two stack entries, and subsequently goes into detail on how types of different sizes are handled during push and pop. What is not so clear is that the same principles apply to local variables too. 4.10.1.4 should introduce the idea that some verification types take up two local variables, and link to 4.10.1.7 where the details are given.