diff --git a/src/utils/boolean_bitfield.rs b/src/utils/boolean_bitfield.rs
index 77323fe048..fd51bff321 100644
--- a/src/utils/boolean_bitfield.rs
+++ b/src/utils/boolean_bitfield.rs
@@ -7,21 +7,25 @@
  * this is just to get the job done for now.
  */
 extern crate rlp;
+use std::cmp::max;
 use self::rlp::{ RlpStream, Encodable };
 
 pub struct BooleanBitfield{
+    len: usize,
     vec: Vec<u8>
 }
 
 impl BooleanBitfield {
     pub fn new() -> Self {
         Self {
+            len: 0,
             vec: vec![]
         }
     }
     
     pub fn with_capacity(capacity: usize) -> Self {
         Self {
+            len: 0,
             vec: Vec::with_capacity(capacity)
         }
     }
@@ -47,6 +51,7 @@ impl BooleanBitfield {
     }
 
     pub fn set_bit(&mut self, bit: &usize, to: &bool) {
+        self.len = max(self.len, *bit + 1);
         self.set_bit_on_byte(*bit % 8, *bit / 8, to);
     }
 
@@ -61,6 +66,8 @@ impl BooleanBitfield {
         }
     }
 
+    pub fn len(&self) -> usize { self.len }
+
     // Return the total number of bits set to true.
     pub fn num_true_bits(&self) -> u64 {
         let mut count: u64 = 0;
@@ -102,6 +109,7 @@ mod tests {
         assert_eq!(b.to_be_vec(), [128]);
         b.set_bit(&7, &false);
         assert_eq!(b.to_be_vec(), [0]);
+        assert_eq!(b.len(), 8);
         
         b = BooleanBitfield::new();
         b.set_bit(&7, &true);
@@ -109,18 +117,21 @@ mod tests {
         assert_eq!(b.to_be_vec(), [129]);
         b.set_bit(&7, &false);
         assert_eq!(b.to_be_vec(), [1]);
+        assert_eq!(b.len(), 8);
         
         b = BooleanBitfield::new();
         b.set_bit(&8, &true);
         assert_eq!(b.to_be_vec(), [1, 0]);
         b.set_bit(&8, &false);
         assert_eq!(b.to_be_vec(), [0, 0]);
+        assert_eq!(b.len(), 9);
         
         b = BooleanBitfield::new();
         b.set_bit(&15, &true);
         assert_eq!(b.to_be_vec(), [128, 0]);
         b.set_bit(&15, &false);
         assert_eq!(b.to_be_vec(), [0, 0]);
+        assert_eq!(b.len(), 16);
         
         b = BooleanBitfield::new();
         b.set_bit(&8, &true);
@@ -128,6 +139,7 @@ mod tests {
         assert_eq!(b.to_be_vec(), [129, 0]);
         b.set_bit(&15, &false);
         assert_eq!(b.to_be_vec(), [1, 0]);
+        assert_eq!(b.len(), 16);
     }
 
     #[test]
diff --git a/src/utils/test_helpers.rs b/src/utils/test_helpers.rs
index da28de63af..8a18496882 100644
--- a/src/utils/test_helpers.rs
+++ b/src/utils/test_helpers.rs
@@ -4,6 +4,8 @@ use super::bls::Keypair;
 use self::rand::thread_rng;
 
 // Returns a keypair for use in testing purposes.
+// It is dangerous because we provide no guarantees
+// that the private key is unique or in-fact private.
 pub fn get_dangerous_test_keypair() -> Keypair {
     let mut rng = thread_rng();
     Keypair::generate(&mut rng)