panic: replaceArg: group fields don't match: 0/16

goroutine 11 [running]:
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a9580?}, {0xe56770?, 0xc0007a96e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:377 +0x425
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a9540?}, {0xe56770?, 0xc0007a96a0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a9520?}, {0xe56770?, 0xc0007a9680?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a9500?}, {0xe56770?, 0xc0007a9660?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a94e0?}, {0xe56770?, 0xc0007a9640?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a94c0?}, {0xe56770?, 0xc0007a9620?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a94a0?}, {0xe56770?, 0xc0007a9600?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.replaceArg({0xe56770?, 0xc0007a9480?}, {0xe56770?, 0xc0007a95e0?})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/prog.go:382 +0x345
github.com/google/syzkaller/prog.(*StructType).mutate(0x16d44a0, 0xc0007a95a0, 0xc0011bc140, {0xe56770, 0xc0007a9460?}, {0xc0011bc0f8, {0x1db72e0, 0x4, 0x4}, 0xc0017df7d0, ...})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:490 +0x185
github.com/google/syzkaller/prog.(*Target).mutateArg(0x418408?, 0xc0005115a0?, 0xc000a17dc8?, {0xe56770, 0xc0007a9460}, {0xc0011bc0f8, {0x1db72e0, 0x4, 0x4}, 0xc0017df7d0, ...}, ...)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:245 +0xe2
github.com/google/syzkaller/prog.(*mutator).mutateArg(0xc000a17e48)
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:196 +0x245
github.com/google/syzkaller/prog.(*Prog).Mutate(0xc001a22040, {0xe52aa8?, 0xc001a5e000}, 0x1e, 0xc0015667c0, 0xc0000a3e90, {0xc000d78000, 0x4f1, 0x500})
	/syzkaller/gopath/src/github.com/google/syzkaller/prog/mutation.go:51 +0x2ba
main.(*Proc).loop(0xc001566800)
	/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