diff --git a/lite/src/types.rs b/lite/src/types.rs
index 08148c032..8a03caa42 100644
--- a/lite/src/types.rs
+++ b/lite/src/types.rs
@@ -37,6 +37,7 @@ pub trait Header {
 /// Validator type which can be used for verifying signatures.
 pub trait ValidatorSet {
     type Validator: Validator;
+    type ValidatorIter: ExactSizeIterator<Item = Self::Validator>;
 
     /// Hash of the validator set.
     fn hash(&self) -> Hash;
@@ -45,8 +46,7 @@ pub trait ValidatorSet {
     fn total_power(&self) -> u64;
 
     /// For iterating over the underlying validators.
-    /// TODO: make this iter()
-    fn into_vec(&self) -> Vec<Self::Validator>;
+    fn iter(&self) -> Self::ValidatorIter;
 }
 
 /// ValidatorSetLookup allows validator to be fetched via their ID
@@ -68,6 +68,7 @@ pub trait Validator {
 /// for verification.
 pub trait Commit {
     type Vote: Vote;
+    type VoteIter: ExactSizeIterator<Item = Option<Self::Vote>>;
 
     /// Hash of the header this commit is for.
     fn header_hash(&self) -> Hash;
@@ -77,7 +78,7 @@ pub trait Commit {
     /// we ignore absent votes and votes for nil here.
     /// NOTE: we may want to check signatures for nil votes,
     /// and thus use an ternary enum here instead of the binary Option.
-    fn into_vec(&self) -> Vec<Option<Self::Vote>>;
+    fn iter(&self) -> Self::VoteIter;
 }
 
 /// Vote contains the data to verify a validator voted correctly in the commit.
diff --git a/lite/src/verifier.rs b/lite/src/verifier.rs
index 8619e534d..91d0ebe6a 100644
--- a/lite/src/verifier.rs
+++ b/lite/src/verifier.rs
@@ -99,18 +99,16 @@ where
     let total_power = vals.total_power();
     let mut signed_power: u64 = 0;
 
-    let vals_vec = vals.into_vec();
-    let commit_vec = commit.into_vec();
+    let vals_iter = vals.iter();
+    let commit_iter = commit.iter();
 
-    if vals_vec.len() != commit_vec.len() {
+    if vals_iter.len() != commit_iter.len() {
         return Err(Error::InvalidCommitLength);
     }
 
     // The vals and commit have a 1-to-1 correspondance.
     // This means we don't need the validator IDs or to do any lookup,
     // we can just zip the iterators.
-    let vals_iter = vals_vec.iter();
-    let commit_iter = commit_vec.iter();
     for (val, vote_opt) in vals_iter.zip(commit_iter) {
         // skip absent and nil votes
         // NOTE: do we want to check the validity of votes
@@ -151,8 +149,7 @@ where
 
     // NOTE we don't know the validators that committed this block,
     // so we have to check for each vote if its validator is already known.
-    let commit_vec = commit.into_vec();
-    let commit_iter = commit_vec.iter();
+    let commit_iter = commit.iter();
     for vote_opt in commit_iter {
         // skip absent and nil votes
         // NOTE: do we want to check the validity of votes