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

goroutine 31 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f3c0?}, {0xe56770?, 0xc0252264c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f3e0?}, {0xe56770?, 0xc025226440?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f400?}, {0xe56770?, 0xc0252263c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f420?}, {0xe56770?, 0xc0252263a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f440?}, {0xe56770?, 0xc025226380?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f460?}, {0xe56770?, 0xc025226360?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f480?}, {0xe56770?, 0xc025226340?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f4a0?}, {0xe56770?, 0xc025226320?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc02505f4c0?}, {0xe56770?, 0xc025226300?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d4620, 0xc02505f2a0, 0xc002a11d10, {0xe56770, 0xc02505f4e0?}, {0xc002a11b88, {0x1db7580, 0x4, 0x4}, 0xc024cc5200, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0x7f0f635ec108?, 0x10?, {0xe56770, 0xc02505f4e0}, {0xc002a11b88, {0x1db7580, 0x4, 0x4}, 0xc024cc5200, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc025341d60)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc01fdc0480, {0xe52aa8?, 0xc0248806c0}, 0x1e, 0xc021858000, 0xc0004ca450, {0xc026380000, 0xdbf0, 0x11000})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).smashInput(0xc021858240, 0xc0254ebfa0)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:221 +0x165
main.(*Proc).loop(0xc021858240)
	/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