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

goroutine 27 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d1a0?}, {0xe56770?, 0xc00078d8c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d160?}, {0xe56770?, 0xc00078d880?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d140?}, {0xe56770?, 0xc00078d860?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d120?}, {0xe56770?, 0xc00078d840?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d100?}, {0xe56770?, 0xc00078d820?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d0e0?}, {0xe56770?, 0xc00078d800?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d0c0?}, {0xe56770?, 0xc00078d7e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00078d080?}, {0xe56770?, 0xc00078d7c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc00078d220, 0xc00158db80, {0xe56770, 0xc00078d060?}, {0xc00158d9f8, {0x1db72e0, 0x4, 0x4}, 0xc0015a3470, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc000c86fc0?, 0xc00127fdc8?, {0xe56770, 0xc00078d060}, {0xc00158d9f8, {0x1db72e0, 0x4, 0x4}, 0xc0015a3470, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00127fe48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0015a1980, {0xe52aa8?, 0xc0010bfcb0}, 0x1e, 0xc00118c480, 0xc0000a3e90, {0xc00084e000, 0x4b4, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc000ec81c0)
	/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