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

goroutine 10 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a51460?}, {0xe56770?, 0xc000a51a80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a51440?}, {0xe56770?, 0xc000a51a60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a51420?}, {0xe56770?, 0xc000a51a40?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a51400?}, {0xe56770?, 0xc000a51a20?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000a513e0?}, {0xe56770?, 0xc000a51a00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc000a51540, 0xc0008f26e0, {0xe56770, 0xc000a513c0?}, {0xc0008f2418, {0x1db72e0, 0x4, 0x4}, 0xc0008f1800, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc00021ed00?, 0xc00cc4bdc8?, {0xe56770, 0xc000a513c0}, {0xc0008f2418, {0x1db72e0, 0x4, 0x4}, 0xc0008f1800, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00cc4be48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc001606f80, {0xe52aa8?, 0xc00111c390}, 0x1e, 0xc00171c000, 0xc000088f00, {0xc00013e000, 0x581, 0x700})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc0016d7500)
	/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