panic: replaceArg: group fields don't match: 0/2

goroutine 12 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0660?}, {0xe56770?, 0xc0009f0c00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0640?}, {0xe56770?, 0xc0009f0be0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0620?}, {0xe56770?, 0xc0009f0bc0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0600?}, {0xe56770?, 0xc0009f0ba0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f05c0?}, {0xe56770?, 0xc0009f0b60?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f05a0?}, {0xe56770?, 0xc0009f0b40?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0560?}, {0xe56770?, 0xc0009f0b00?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0540?}, {0xe56770?, 0xc0009f0ae0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0520?}, {0xe56770?, 0xc0009f0ac0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f0500?}, {0xe56770?, 0xc0009f0aa0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0009f04e0?}, {0xe56770?, 0xc0009f0a80?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc0009f0700, 0xc00b935f90, {0xe56770, 0xc0009f04c0?}, {0xc00b935ef8, {0x1db72e0, 0x4, 0x4}, 0xc00ba5e4b0, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x0?, 0xc000e587e0?, 0xc0009dddc8?, {0xe56770, 0xc0009f04c0}, {0xc00b935ef8, {0x1db72e0, 0x4, 0x4}, 0xc00ba5e4b0, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc0009dde48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc00ba5afc0, {0xe52aa8?, 0xc00123c270}, 0x1e, 0xc00160e140, 0xc00007af00, {0xc0000ce000, 0x51a, 0x700})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc00160e400)
	/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