diff --git a/consensus/reactor.go b/consensus/reactor.go
index 7208f397a..80e87efd8 100644
--- a/consensus/reactor.go
+++ b/consensus/reactor.go
@@ -584,6 +584,8 @@ OUTER_LOOP:
 	}
 }
 
+// NOTE: `queryMaj23Routine` has a simple crude design since it only comes
+// into play for liveness when there's a signature DDoS attack happening.
 func (conR *ConsensusReactor) queryMaj23Routine(peer *p2p.Peer, ps *PeerState) {
 	log := log.New("peer", peer)
 
diff --git a/types/vote_set.go b/types/vote_set.go
index a1a2bf394..de853a5e7 100644
--- a/types/vote_set.go
+++ b/types/vote_set.go
@@ -122,7 +122,11 @@ func (voteSet *VoteSet) Size() int {
 // Duplicate votes return added=false, err=nil.
 // Conflicting votes return added=*, err=ErrVoteConflictingVotes.
 // NOTE: vote should not be mutated after adding.
+// NOTE: VoteSet must not be nil
 func (voteSet *VoteSet) AddVote(vote *Vote) (added bool, err error) {
+	if voteSet == nil {
+		PanicSanity("AddVote() on nil VoteSet")
+	}
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 
@@ -276,7 +280,11 @@ func (voteSet *VoteSet) addVerifiedVote(vote *Vote, blockKey string, votingPower
 // NOTE: if there are too many peers, or too much peer churn,
 // this can cause memory issues.
 // TODO: implement ability to remove peers too
+// NOTE: VoteSet must not be nil
 func (voteSet *VoteSet) SetPeerMaj23(peerID string, blockID BlockID) {
+	if voteSet == nil {
+		PanicSanity("SetPeerMaj23() on nil VoteSet")
+	}
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 
@@ -332,12 +340,18 @@ func (voteSet *VoteSet) BitArrayByBlockID(blockID BlockID) *BitArray {
 
 // NOTE: if validator has conflicting votes, returns "canonical" vote
 func (voteSet *VoteSet) GetByIndex(valIndex int) *Vote {
+	if voteSet == nil {
+		return nil
+	}
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 	return voteSet.votes[valIndex]
 }
 
 func (voteSet *VoteSet) GetByAddress(address []byte) *Vote {
+	if voteSet == nil {
+		return nil
+	}
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 	valIndex, val := voteSet.valSet.GetByAddress(address)
@@ -384,6 +398,9 @@ func (voteSet *VoteSet) HasAll() bool {
 // Returns either a blockhash (or nil) that received +2/3 majority.
 // If there exists no such majority, returns (nil, PartSetHeader{}, false).
 func (voteSet *VoteSet) TwoThirdsMajority() (blockID BlockID, ok bool) {
+	if voteSet == nil {
+		return BlockID{}, false
+	}
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 	if voteSet.maj23 != nil {