panic: replaceArg: group fields don't match: 0/1

goroutine 14 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cdee0?}, {0xe56770?, 0xc0006e40a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cdec0?}, {0xe56770?, 0xc0006e4080?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cdea0?}, {0xe56770?, 0xc0006e4060?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cde80?}, {0xe56770?, 0xc0006e4040?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cde60?}, {0xe56770?, 0xc0006e4020?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cde40?}, {0xe56770?, 0xc0006e4000?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cde20?}, {0xe56770?, 0xc0006cdfe0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0006cde00?}, {0xe56770?, 0xc0006cdfc0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc0006cdf80, 0xc0010b76d0, {0xe56770, 0xc0006cdde0?}, {0xc0010b7688, {0x1db72e0, 0x4, 0x4}, 0xc001233f80, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0x0?, 0x8b7dc8?, {0xe56770, 0xc0006cdde0}, {0xc0010b7688, {0x1db72e0, 0x4, 0x4}, 0xc001233f80, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc0008b7e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc001275880, {0xe52aa8?, 0xc0017dda40}, 0x1e, 0xc00176c040, 0xc000097e90, {0xc000988000, 0x41f, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc001144640)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:95 +0x365
created by main.main in goroutine 1
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:336 +0x1665