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

goroutine 23 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a89960?}, {0xe56770?, 0xc000a89c40?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a898e0?}, {0xe56770?, 0xc000a89bc0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a89860?}, {0xe56770?, 0xc000a89b40?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a89840?}, {0xe56770?, 0xc000a89b20?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a89820?}, {0xe56770?, 0xc000a89b00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a89800?}, {0xe56770?, 0xc000a89ae0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a897e0?}, {0xe56770?, 0xc000a89ac0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a897c0?}, {0xe56770?, 0xc000a89aa0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a897a0?}, {0xe56770?, 0xc000a89a80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d4620, 0xc000a89a40, 0xc00cfc01e0, {0xe56770, 0xc000a89780?}, {0xc00cfc0148, {0x1db7580, 0x4, 0x4}, 0xc00cfb9350, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0xc0003b12c0?, 0xc0007afdc8?, {0xe56770, 0xc000a89780}, {0xc00cfc0148, {0x1db7580, 0x4, 0x4}, 0xc00cfb9350, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc0007afe48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00cfbc880, {0xe52aa8?, 0xc0015fc000}, 0x1e, 0xc0012b0000, 0xc000113dd0, {0xc00013e000, 0x590, 0x700})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc0012b0040)
	/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