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

goroutine 13 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f620?}, {0xe56770?, 0xc00059f7e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f600?}, {0xe56770?, 0xc00059f7c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f5e0?}, {0xe56770?, 0xc00059f7a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f5c0?}, {0xe56770?, 0xc00059f780?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f5a0?}, {0xe56770?, 0xc00059f760?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f580?}, {0xe56770?, 0xc00059f740?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f560?}, {0xe56770?, 0xc00059f720?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00059f540?}, {0xe56770?, 0xc00059f700?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc00059f6c0, 0xc00b4e14f0, {0xe56770, 0xc00059f520?}, {0xc00b4e1408, {0x1db72e0, 0x4, 0x4}, 0xc00b5eac60, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x7f1ad5d32248?, 0x7f1b1ce97108?, 0x10?, {0xe56770, 0xc00059f520}, {0xc00b4e1408, {0x1db72e0, 0x4, 0x4}, 0xc00b5eac60, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00b703e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00b68e640, {0xe52aa8?, 0xc0012ea300}, 0x1e, 0xc000e7a0c0, 0xc000113e90, {0xc000c5a000, 0x414, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc000e7a100)
	/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