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

goroutine 9 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a340?}, {0xe61b40?, 0xc01013bac0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x459
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a280?}, {0xe61b40?, 0xc01013b9e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a120?}, {0xe61b40?, 0xc01013b920?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a100?}, {0xe61b40?, 0xc01013b8e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a0e0?}, {0xe61b40?, 0xc01013b840?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a0c0?}, {0xe61b40?, 0xc01013b820?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a0a0?}, {0xe61b40?, 0xc01013b800?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a080?}, {0xe61b40?, 0xc01013b7e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.replaceArg({0xe61b40?, 0xc01013a060?}, {0xe61b40?, 0xc01013b7c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x36c
github.com/google/syzkaller/prog.(*StructType).mutate(0x15f23e0, 0xc01013a3c0, 0xc014a7e690, {0xe61b40, 0xc01013a040?}, {0xc014a7e3c8, {0x1d2ea60, 0x4, 0x4}, 0xc014807ef0, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x189
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0x415cb0?, 0xc000adfdc8?, {0xe61b40, 0xc01013a040}, {0xc014a7e3c8, {0x1d2ea60, 0x4, 0x4}, 0xc014807ef0, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xed
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000adfe48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x28c
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc010c19240, {0xe5ee08?, 0xc00df0ea80}, 0x1e, 0xc0119fa080, 0xc0004d5620, {0xc00f5fe000, 0x94a0, 0xac00})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2d6
main.(*Proc).loop(0xc0119fa0c0)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:95 +0x365
created by main.main
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:336 +0x1685