diff --git a/light-client/src/operations/voting_power.rs b/light-client/src/operations/voting_power.rs
index 954b2c54d..b417e59e7 100644
--- a/light-client/src/operations/voting_power.rs
+++ b/light-client/src/operations/voting_power.rs
@@ -1,7 +1,10 @@
 use crate::prelude::*;
 
 use anomaly::BoxError;
+
+use tendermint::block::CommitSig;
 use tendermint::lite::types::ValidatorSet as _;
+use tendermint::vote::{SignedVote, Vote};
 
 pub trait VotingPowerCalculator {
     fn total_power_of(&self, validators: &ValidatorSet) -> u64;
@@ -50,36 +53,104 @@ impl VotingPowerCalculator for ProdVotingPowerCalculator {
     fn voting_power_in(
         &self,
         signed_header: &SignedHeader,
-        validators: &ValidatorSet,
+        validator_set: &ValidatorSet,
     ) -> Result<u64, BoxError> {
+        let signatures = &signed_header.commit.signatures;
+        let validators = validator_set.validators();
+
+        // ensure!(
+        //     validators.len() == signatures.len(),
+        //     // TODO: Raise error
+        // );
+
         // 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 mut signed_power = 0_u64;
+        let voting_power_needed = self.total_power_of(validator_set) * 2 / 3;
+        let mut tallied_voting_power = 0_u64;
+
+        for (idx, signature) in signatures.into_iter().enumerate() {
+            if signature.is_absent() {
+                continue; // OK, some signatures can be absent.
+            }
+
+            // The vals and commit have a 1-to-1 correspondance (see check above).
+            // This means we don't need the validator address or to do any lookup.
+            let val = validators[idx];
 
-        for vote in &signed_header.signed_votes() {
-            // Only count if this vote is from a known validator.
-            // TODO: we still need to check that we didn't see a vote from this validator twice ...
-            let val_id = vote.validator_id();
-            let val = match validators.validator(val_id) {
-                Some(v) => v,
-                None => continue,
-            };
+            let vote = vote_from_non_absent_signature(signature, idx as u64, &signed_header.commit)
+                .unwrap(); // SAFETY: Safe because of `is_absent()` check above.
 
-            // check vote is valid from validator
-            let sign_bytes = vote.sign_bytes();
+            let signed_vote = SignedVote::new(
+                (&vote).into(),
+                signed_header.header.chain_id.as_str(),
+                vote.validator_address,
+                vote.signature,
+            );
 
-            if !val.verify_signature(&sign_bytes, vote.signature()) {
+            // Check vote is valid from validator
+            let sign_bytes = signed_vote.sign_bytes();
+            if !val.verify_signature(&sign_bytes, signed_vote.signature()) {
                 bail!(VerificationError::ImplementationSpecific(format!(
                     "Couldn't verify signature {:?} with validator {:?} on sign_bytes {:?}",
-                    vote.signature(),
+                    signed_vote.signature(),
                     val,
                     sign_bytes,
                 )));
             }
 
-            signed_power += val.power();
+            if signature.is_commit() {
+                tallied_voting_power += val.power();
+            } else {
+                // It's OK. We include stray signatures (~votes for nil) to measure
+                // validator availability.
+            }
+
+            if tallied_voting_power >= voting_power_needed {
+                break;
+            }
         }
 
-        Ok(signed_power)
+        Ok(tallied_voting_power)
     }
 }
+
+fn vote_from_non_absent_signature(
+    commit_sig: &CommitSig,
+    validator_index: u64,
+    commit: &Commit,
+) -> Option<Vote> {
+    let (validator_address, timestamp, signature, block_id) = match commit_sig {
+        CommitSig::BlockIDFlagAbsent { .. } => return None,
+        CommitSig::BlockIDFlagCommit {
+            validator_address,
+            timestamp,
+            signature,
+        } => (
+            validator_address.clone(),
+            timestamp.clone(),
+            signature.clone(),
+            Some(commit.block_id.clone()),
+        ),
+        CommitSig::BlockIDFlagNil {
+            validator_address,
+            timestamp,
+            signature,
+        } => (
+            validator_address.clone(),
+            timestamp.clone(),
+            signature.clone(),
+            None,
+        ),
+    };
+
+    Some(Vote {
+        vote_type: tendermint::vote::Type::Precommit,
+        height: commit.height,
+        round: commit.round,
+        block_id,
+        timestamp,
+        validator_address,
+        validator_index,
+        signature,
+    })
+}
diff --git a/tendermint/src/block/commit_sig.rs b/tendermint/src/block/commit_sig.rs
index c8b83e9c9..93f68910d 100644
--- a/tendermint/src/block/commit_sig.rs
+++ b/tendermint/src/block/commit_sig.rs
@@ -34,6 +34,29 @@ pub enum CommitSig {
     },
 }
 
+impl CommitSig {
+    /// Whether this signature is absent (no vote was received from validator)
+    pub fn is_absent(&self) -> bool {
+        self == &Self::BlockIDFlagAbsent
+    }
+
+    /// Whether this signature is a commit  (validator voted for the Commit.BlockId)
+    pub fn is_commit(&self) -> bool {
+        match self {
+            Self::BlockIDFlagCommit { .. } => true,
+            _ => false,
+        }
+    }
+
+    /// Whether this signature is nil (validator voted for nil)
+    pub fn is_nil(&self) -> bool {
+        match self {
+            Self::BlockIDFlagNil { .. } => true,
+            _ => false,
+        }
+    }
+}
+
 // Todo: https://github.com/informalsystems/tendermint-rs/issues/259 - CommitSig Timestamp can be zero time
 // Todo: https://github.com/informalsystems/tendermint-rs/issues/260 - CommitSig validator address missing in Absent vote
 impl TryFrom<RawCommitSig> for CommitSig {