diff --git a/eth2/utils/ssz_types/src/bitfield.rs b/eth2/utils/ssz_types/src/bitfield.rs
index b7cdb2876..1cb53ab1e 100644
--- a/eth2/utils/ssz_types/src/bitfield.rs
+++ b/eth2/utils/ssz_types/src/bitfield.rs
@@ -71,8 +71,10 @@ pub struct Bitfield<T> {
 impl<N: Unsigned + Clone> Bitfield<BitList<N>> {
     pub fn with_capacity(num_bits: usize) -> Option<Self> {
         if num_bits <= N::to_usize() {
+            let num_bytes = std::cmp::max(bytes_for_bit_len(num_bits), 1);
+
             Some(Self {
-                bytes: vec![0; bytes_for_bit_len(num_bits)],
+                bytes: vec![0; num_bytes],
                 len: num_bits,
                 _phantom: PhantomData,
             })
@@ -81,7 +83,7 @@ impl<N: Unsigned + Clone> Bitfield<BitList<N>> {
         }
     }
 
-    pub fn capacity() -> usize {
+    pub fn max_len() -> usize {
         N::to_usize()
     }
 
@@ -89,15 +91,13 @@ impl<N: Unsigned + Clone> Bitfield<BitList<N>> {
         let len = self.len();
         let mut bytes = self.as_slice().to_vec();
 
-        if bytes_for_bit_len(len + 1) == bytes.len() + 1 {
+        while bytes_for_bit_len(len + 1) > bytes.len() {
             bytes.insert(0, 0);
         }
 
         let mut bitfield: Bitfield<BitList<N>> = Bitfield::from_raw_bytes(bytes, len + 1)
             .expect("Bitfield capacity has been confirmed earlier.");
-        bitfield
-            .set(len, true)
-            .expect("Bitfield capacity has been confirmed earlier.");
+        bitfield.set(len, true).expect("Bitfield index must exist.");
 
         bitfield.bytes
     }
@@ -110,17 +110,22 @@ impl<N: Unsigned + Clone> Bitfield<BitList<N>> {
         };
 
         let len = initial_bitfield.highest_set_bit()?;
-        initial_bitfield
-            .set(len, false)
-            .expect("Bit has been confirmed to exist");
 
-        let mut bytes = initial_bitfield.to_raw_bytes();
+        if len <= Self::max_len() {
+            initial_bitfield
+                .set(len, false)
+                .expect("Bit has been confirmed to exist");
 
-        if bytes_for_bit_len(len) < bytes.len() {
-            bytes.remove(0);
+            let mut bytes = initial_bitfield.to_raw_bytes();
+
+            if bytes_for_bit_len(len) < bytes.len() && bytes != &[0] {
+                bytes.remove(0);
+            }
+
+            Self::from_raw_bytes(bytes, len)
+        } else {
+            None
         }
-
-        Self::from_raw_bytes(bytes, len)
     }
 }
 
@@ -203,7 +208,7 @@ impl<T: BitfieldBehaviour> Bitfield<T> {
         &self.bytes
     }
 
-    pub fn from_raw_bytes(bytes: Vec<u8>, bit_len: usize) -> Option<Self> {
+    fn from_raw_bytes(bytes: Vec<u8>, bit_len: usize) -> Option<Self> {
         if bytes.len() == 1 && bit_len == 0 && bytes == &[0] {
             // A bitfield with `bit_len` 0 can only be represented by a single zero byte.
             Some(Self {
@@ -552,7 +557,137 @@ impl<N: Unsigned + Clone> cached_tree_hash::CachedTreeHash for Bitfield<BitVecto
 mod test {
     use super::*;
 
-    type Bitfield = super::Bitfield<BitList<typenum::U1024>>;
+    mod bitlist {
+        use super::*;
+
+        pub type BitList<N> = crate::Bitfield<crate::BitList<N>>;
+        pub type BitList0 = BitList<typenum::U0>;
+        pub type BitList1 = BitList<typenum::U1>;
+        pub type BitList8 = BitList<typenum::U8>;
+        pub type BitList16 = BitList<typenum::U16>;
+
+        #[test]
+        fn ssz_encode() {
+            assert_eq!(
+                BitList0::with_capacity(0).unwrap().as_ssz_bytes(),
+                vec![0b0000_00001],
+            );
+
+            assert_eq!(
+                BitList1::with_capacity(0).unwrap().as_ssz_bytes(),
+                vec![0b0000_00001],
+            );
+
+            assert_eq!(
+                BitList1::with_capacity(1).unwrap().as_ssz_bytes(),
+                vec![0b0000_00010],
+            );
+
+            assert_eq!(
+                BitList8::with_capacity(8).unwrap().as_ssz_bytes(),
+                vec![0b0000_0001, 0b0000_0000],
+            );
+
+            assert_eq!(
+                BitList8::with_capacity(7).unwrap().as_ssz_bytes(),
+                vec![0b1000_0000]
+            );
+
+            let mut b = BitList8::with_capacity(8).unwrap();
+            for i in 0..8 {
+                b.set(i, true).unwrap();
+            }
+            assert_eq!(b.as_ssz_bytes(), vec![0b0000_0001, 255]);
+
+            let mut b = BitList8::with_capacity(8).unwrap();
+            for i in 0..4 {
+                b.set(i, true).unwrap();
+            }
+            assert_eq!(b.as_ssz_bytes(), vec![0b0000_0001, 0b0000_1111]);
+
+            assert_eq!(
+                BitList16::with_capacity(16).unwrap().as_ssz_bytes(),
+                vec![0b0000_0001, 0b0000_0000, 0b0000_0000]
+            );
+        }
+
+        #[test]
+        fn ssz_decode() {
+            assert!(BitList0::from_ssz_bytes(&[0b0000_0000]).is_err());
+            assert!(BitList1::from_ssz_bytes(&[0b0000_0000, 0b0000_0000]).is_err());
+            assert!(BitList8::from_ssz_bytes(&[0b0000_0000]).is_err());
+            assert!(BitList16::from_ssz_bytes(&[0b0000_0000]).is_err());
+
+            assert!(BitList0::from_ssz_bytes(&[0b0000_0001]).is_ok());
+            assert!(BitList0::from_ssz_bytes(&[0b0000_0010]).is_err());
+
+            assert!(BitList1::from_ssz_bytes(&[0b0000_0001]).is_ok());
+            assert!(BitList1::from_ssz_bytes(&[0b0000_0010]).is_ok());
+            assert!(BitList1::from_ssz_bytes(&[0b0000_0100]).is_err());
+
+            assert!(BitList8::from_ssz_bytes(&[0b0000_0001]).is_ok());
+            assert!(BitList8::from_ssz_bytes(&[0b0000_0010]).is_ok());
+            assert!(BitList8::from_ssz_bytes(&[0b0000_0001, 0b0000_0100]).is_ok());
+            assert!(BitList8::from_ssz_bytes(&[0b0000_0010, 0b0000_0100]).is_err());
+        }
+
+        #[test]
+        fn ssz_round_trip() {
+            assert_round_trip(BitList0::with_capacity(0).unwrap());
+
+            for i in 0..2 {
+                assert_round_trip(BitList1::with_capacity(i).unwrap());
+            }
+            for i in 0..9 {
+                assert_round_trip(BitList8::with_capacity(i).unwrap());
+            }
+            for i in 0..17 {
+                assert_round_trip(BitList16::with_capacity(i).unwrap());
+            }
+
+            let mut b = BitList1::with_capacity(1).unwrap();
+            b.set(0, true);
+            assert_round_trip(b);
+
+            for i in 0..8 {
+                let mut b = BitList8::with_capacity(i).unwrap();
+                for j in 0..i {
+                    if j % 2 == 0 {
+                        b.set(j, true);
+                    }
+                }
+                assert_round_trip(b);
+
+                let mut b = BitList8::with_capacity(i).unwrap();
+                for j in 0..i {
+                    b.set(j, true);
+                }
+                assert_round_trip(b);
+            }
+
+            for i in 0..16 {
+                let mut b = BitList16::with_capacity(i).unwrap();
+                for j in 0..i {
+                    if j % 2 == 0 {
+                        b.set(j, true);
+                    }
+                }
+                assert_round_trip(b);
+
+                let mut b = BitList16::with_capacity(i).unwrap();
+                for j in 0..i {
+                    b.set(j, true);
+                }
+                assert_round_trip(b);
+            }
+        }
+
+        fn assert_round_trip<T: Encode + Decode + PartialEq + std::fmt::Debug>(t: T) {
+            assert_eq!(T::from_ssz_bytes(&t.as_ssz_bytes()).unwrap(), t);
+        }
+    }
+
+    type Bitfield = crate::Bitfield<BitList<typenum::U1024>>;
 
     #[test]
     fn from_raw_bytes() {