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

goroutine 16 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0008235c0?}, {0xe56770?, 0xc0008237c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0008235a0?}, {0xe56770?, 0xc0008237a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000823580?}, {0xe56770?, 0xc000823780?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000823560?}, {0xe56770?, 0xc000823760?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000823540?}, {0xe56770?, 0xc000823740?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000823520?}, {0xe56770?, 0xc000823720?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000823500?}, {0xe56770?, 0xc000823700?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0008234e0?}, {0xe56770?, 0xc0008236e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc000823600, 0xc000a47ef0, {0xe56770, 0xc0008234c0?}, {0xc000a47e58, {0x1db72e0, 0x4, 0x4}, 0xc00c246870, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc000e19860?, 0xc00c44ddc8?, {0xe56770, 0xc0008234c0}, {0xc000a47e58, {0x1db72e0, 0x4, 0x4}, 0xc00c246870, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00c44de48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0016eb180, {0xe52aa8?, 0xc0014141b0}, 0x1e, 0xc001ad2000, 0xc0000a2930, {0xc001180000, 0x4ce, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc001ad2300)
	/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