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

goroutine 12 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bcc0?}, {0xe56770?, 0xc00080bf00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bc40?}, {0xe56770?, 0xc00080be80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bbc0?}, {0xe56770?, 0xc00080be00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bba0?}, {0xe56770?, 0xc00080bde0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bb80?}, {0xe56770?, 0xc00080bdc0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bb60?}, {0xe56770?, 0xc00080bda0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bb40?}, {0xe56770?, 0xc00080bd80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bb20?}, {0xe56770?, 0xc00080bd60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00080bb00?}, {0xe56770?, 0xc00080bd40?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d4620, 0xc00080bd00, 0xc00b745310, {0xe56770, 0xc00080bae0?}, {0xc00b7452c8, {0x1db7580, 0x4, 0x4}, 0xc00b836d50, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0xc00011dc00?, 0xc000773dc8?, {0xe56770, 0xc00080bae0}, {0xc00b7452c8, {0x1db7580, 0x4, 0x4}, 0xc00b836d50, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000773e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00b852780, {0xe52aa8?, 0xc0012b8120}, 0x1e, 0xc0014c41c0, 0xc0000a3950, {0xc001298000, 0x41f, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc0014c4280)
	/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