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

goroutine 27 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000916fa0?}, {0xe56770?, 0xc0009171a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000916f80?}, {0xe56770?, 0xc000917180?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000916f60?}, {0xe56770?, 0xc000917160?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000916f40?}, {0xe56770?, 0xc000917140?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000916f20?}, {0xe56770?, 0xc000917120?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc000917040, 0xc00c4c57c0, {0xe56770, 0xc000916f00?}, {0xc00c4c5728, {0x1db72e0, 0x4, 0x4}, 0xc00c69a180, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc000d275e0?, 0xc00056fdc8?, {0xe56770, 0xc000916f00}, {0xc00c4c5728, {0x1db72e0, 0x4, 0x4}, 0xc00c69a180, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00056fe48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00c69c2c0, {0xe52aa8?, 0xc0016fc210}, 0x1e, 0xc00152e1c0, 0xc000547260, {0xc001462000, 0x41e, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc00152e340)
	/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