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

goroutine 9 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785d20?}, {0xe56770?, 0xc000785fc0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785d00?}, {0xe56770?, 0xc000785fa0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785ce0?}, {0xe56770?, 0xc000785f80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785cc0?}, {0xe56770?, 0xc000785f60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785c80?}, {0xe56770?, 0xc000785f20?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785c60?}, {0xe56770?, 0xc000785f00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785c40?}, {0xe56770?, 0xc000785ee0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785c20?}, {0xe56770?, 0xc000785ec0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785c00?}, {0xe56770?, 0xc000785ea0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785be0?}, {0xe56770?, 0xc000785e80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc000785bc0?}, {0xe56770?, 0xc000785e60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc000785d60, 0xc00184d0e0, {0xe56770, 0xc000785ba0?}, {0xc00184d048, {0x1db72e0, 0x4, 0x4}, 0xc001cf6570, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc0003c93e0?, 0xc000ed1dc8?, {0xe56770, 0xc000785ba0}, {0xc00184d048, {0x1db72e0, 0x4, 0x4}, 0xc001cf6570, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000ed1e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc001c92e40, {0xe52aa8?, 0xc000cec330}, 0x1e, 0xc001aec0c0, 0xc000088810, {0xc00075c000, 0x4a7, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc001aec340)
	/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