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

goroutine 25 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a13e0?}, {0xe56770?, 0xc000b200c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a09c0?}, {0xe56770?, 0xc000891ba0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0940?}, {0xe56770?, 0xc000891b20?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0920?}, {0xe56770?, 0xc000891b00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0900?}, {0xe56770?, 0xc000891ae0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0560?}, {0xe56770?, 0xc000891ac0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0540?}, {0xe56770?, 0xc000891aa0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0520?}, {0xe56770?, 0xc000891a80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0005a0500?}, {0xe56770?, 0xc000891a60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d4620, 0xc0005a1f20, 0xc002644b90, {0xe56770, 0xc0005a04e0?}, {0xc00159d228, {0x1db7580, 0x4, 0x4}, 0xc0012da8a0, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x7f4292c8f030?, 0x7f42e0228108?, 0x80?, {0xe56770, 0xc0005a04e0}, {0xc00159d228, {0x1db7580, 0x4, 0x4}, 0xc0012da8a0, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000b97d60)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0013511c0, {0xe52aa8?, 0xc00091a180}, 0x1e, 0xc00057c580, 0xc000088f90, {0xc0015c6800, 0x409, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).smashInput(0xc00090d900, 0xc0017fb970)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:221 +0x165
main.(*Proc).loop(0xc00090d900)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:78 +0xf2
created by main.main in goroutine 1
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:336 +0x1665