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

goroutine 28 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e8c0?}, {0xe56770?, 0xc00082ea20?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e8a0?}, {0xe56770?, 0xc00082ea00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e880?}, {0xe56770?, 0xc00082e9e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e860?}, {0xe56770?, 0xc00082e9c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e840?}, {0xe56770?, 0xc00082e9a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e820?}, {0xe56770?, 0xc00082e980?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e800?}, {0xe56770?, 0xc00082e960?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc00082e7e0?}, {0xe56770?, 0xc00082e940?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc00082e900, 0xc001673bd0, {0xe56770, 0xc00082e7c0?}, {0xc001673b88, {0x1db72e0, 0x4, 0x4}, 0xc000ae2480, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0xc00059f660?, 0xc0005f3dc8?, {0xe56770, 0xc00082e7c0}, {0xc001673b88, {0x1db72e0, 0x4, 0x4}, 0xc000ae2480, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc00084fe48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc0017d4480, {0xe52aa8?, 0xc0009ea090}, 0x1e, 0xc0011f23c0, 0xc0000a37d0, {0xc000550000, 0x530, 0x700})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc0019e7e00)
	/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