panic: broken type ref

goroutine 39 [running]:
github.com/google/syzkaller/prog.ArgCommon.Type(...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:69
github.com/google/syzkaller/prog.(*serializer).call(0xc0009d8690, 0xc00035bdb0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/encoding.go:76 +0x1aa
github.com/google/syzkaller/prog.(*Prog).serialize(0xc0007bb2c0, 0x0)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/encoding.go:46 +0xd8
github.com/google/syzkaller/prog.(*Prog).Serialize(...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/encoding.go:30
main.(*Proc).logProgram(0xc00038a900, 0xc0007bb2c0)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:130 +0x4e
main.(*Proc).executeRaw(0xc00038a900, 0xc0005a9ef0, 0xc0007bb2c0)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:101 +0x125
main.(*Proc).loop(0xc00038a900)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:65 +0x148
created by main.main in goroutine 1
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:256 +0x118a