error: cannot find derive macro `BitfieldStruct` in this scope

[ctaggart]

The latest from master fails to compile with:

Camerons-MacBook-Pro:openconnect-rust cameron$ cargo build
   Compiling openconnect-rust v0.0.0 (/Users/cameron/github/openconnect-rust)
error: cannot find derive macro `BitfieldStruct` in this scope
    --> src/tun.rs:1198:29
     |
1198 |     #[derive ( Copy, Clone, BitfieldStruct )]
     |                             ^^^^^^^^^^^^^^

error: cannot find derive macro `BitfieldStruct` in this scope
    --> src/gpst.rs:1086:29
     |
1086 |     #[derive ( Copy, Clone, BitfieldStruct )]
     |                             ^^^^^^^^^^^^^^

It is complaining about:

openconnect-rust/src/tun.rs

Lines 1198 to 1215 in 28ff0a3

	#[derive ( Copy, Clone, BitfieldStruct )]
	#[repr(C)]
	#[src_loc = "81:1"]
	pub struct ip {
	#[bitfield(name = "ip_hl", ty = "u_int", bits = "0..=3")]
	#[bitfield(name = "ip_v", ty = "u_int", bits = "4..=7")]
	pub ip_hl_ip_v: [u8; 1],
	pub ip_tos: u_char,
	pub ip_len: u_short,
	pub ip_id: u_short,
	pub ip_off: u_short,
	pub ip_ttl: u_char,
	pub ip_p: u_char,
	pub ip_sum: u_short,
	pub ip_src: in_addr,
	pub ip_dst: in_addr,
	/* source and dest address */
	}

I tried to manually fix it for about a half hour and wasn't able to.