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

goroutine 11 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bf20?}, {0xe56770?, 0xc001d8f880?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bea0?}, {0xe56770?, 0xc001d8f800?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0be20?}, {0xe56770?, 0xc001d8f780?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0be00?}, {0xe56770?, 0xc001d8f760?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bde0?}, {0xe56770?, 0xc001d8f740?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bdc0?}, {0xe56770?, 0xc001d8f720?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bda0?}, {0xe56770?, 0xc001d8f700?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bd80?}, {0xe56770?, 0xc001d8f6e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000b0bd60?}, {0xe56770?, 0xc001d8f6c0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d4620, 0xc000b0bf40, 0xc002442050, {0xe56770, 0xc000b0bd40?}, {0xc001a01d18, {0x1db7580, 0x4, 0x4}, 0xc006a15b90, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc0028a3520?, 0xc001be7ce0?, {0xe56770, 0xc000b0bd40}, {0xc001a01d18, {0x1db7580, 0x4, 0x4}, 0xc006a15b90, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc001be7d60)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc001bca7c0, {0xe52aa8?, 0xc00100b320}, 0x1e, 0xc000824080, 0xc0000a3f50, {0xc001db4000, 0x173, 0x200})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).smashInput(0xc000824d80, 0xc001525b50)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:221 +0x165
main.(*Proc).loop(0xc000824d80)
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/proc.go:78 +0xf2
created by main.main in goroutine 1
	/syzkaller/gopath/src/github.com/google/syzkaller/syz-fuzzer/fuzzer.go:336 +0x1665