panic: replaceArg: group fields don't match: 0/2

goroutine 13 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b0c0?}, {0xe56770?, 0xc00071b340?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b0a0?}, {0xe56770?, 0xc00071b320?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b080?}, {0xe56770?, 0xc00071b2e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b060?}, {0xe56770?, 0xc00071b2c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b040?}, {0xe56770?, 0xc00071b2a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b020?}, {0xe56770?, 0xc00071b280?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071b000?}, {0xe56770?, 0xc00071b260?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00071afe0?}, {0xe56770?, 0xc00071b240?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc00071b200, 0xc00c2ef090, {0xe56770, 0xc00071afc0?}, {0xc00c2ef048, {0x1db72e0, 0x4, 0x4}, 0xc00c775a10, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0xc0003f6f40?, 0xc000969dc8?, {0xe56770, 0xc00071afc0}, {0xc00c2ef048, {0x1db72e0, 0x4, 0x4}, 0xc00c775a10, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000969e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0010517c0, {0xe52aa8?, 0xc001382390}, 0x1e, 0xc00126e0c0, 0xc000088f00, {0xc0016e0000, 0x41b, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc00126e180)
	/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