diff --git a/ledger/apply/heartbeat.go b/ledger/apply/heartbeat.go
index 1c8a55f4b9..bce788cf68 100644
--- a/ledger/apply/heartbeat.go
+++ b/ledger/apply/heartbeat.go
@@ -28,10 +28,13 @@ import (
 func Heartbeat(hb transactions.HeartbeatTxnFields, header transactions.Header, balances Balances, provider HdrProvider, round basics.Round) error {
 	// Get the account's balance entry
 	account, err := balances.Get(hb.HeartbeatAddress, false)
+	if err != nil {
+		return err
+	}
 
 	sv := account.VoteID
 	if sv.IsEmpty() {
-		return fmt.Errorf("HeartbeatAddress %s has has no voting keys\n", hb.HeartbeatAddress)
+		return fmt.Errorf("heartbeat address %s has no voting keys\n", hb.HeartbeatAddress)
 	}
 	id := basics.OneTimeIDForRound(header.LastValid, account.VoteKeyDilution)
 
diff --git a/ledger/apply/mockBalances_test.go b/ledger/apply/mockBalances_test.go
index dd77b66e7f..91f918cf80 100644
--- a/ledger/apply/mockBalances_test.go
+++ b/ledger/apply/mockBalances_test.go
@@ -291,5 +291,5 @@ func (m mockHeaders) BlockHdr(r basics.Round) (bookkeeping.BlockHeader, error) {
 	if hdr, ok := m.b[r]; ok {
 		return hdr, nil
 	}
-	return bookkeeping.BlockHeader{}, fmt.Errorf("Round %v is not present\n", r)
+	return bookkeeping.BlockHeader{}, fmt.Errorf("round %v is not present\n", r)
 }
diff --git a/ledger/eval/eval.go b/ledger/eval/eval.go
index 419a960692..0014bc0044 100644
--- a/ledger/eval/eval.go
+++ b/ledger/eval/eval.go
@@ -1712,6 +1712,9 @@ type headerSource interface {
 	BlockHdr(round basics.Round) (bookkeeping.BlockHeader, error)
 }
 
+// ActiveChallenge returns details about the Challenge that was last issued if
+// it is still in effect (that is, between one and two grace periods from
+// issue). Otherwise it returns the zero value.
 func ActiveChallenge(rules config.ProposerPayoutRules, current basics.Round, headers headerSource) challenge {
 	// are challenges active?
 	interval := basics.Round(rules.ChallengeInterval)
@@ -1736,6 +1739,8 @@ func ActiveChallenge(rules config.ProposerPayoutRules, current basics.Round, hea
 	return challenge{lastChallenge, challengeHdr.Seed, rules.ChallengeBits}
 }
 
+// FailsChallenge returns true iff ch is in effect, matches address, and
+// lastSeen is before the challenge issue.
 func FailsChallenge(ch challenge, address basics.Address, lastSeen basics.Round) bool {
 	return ch.round != 0 && bitsMatch(ch.seed[:], address[:], ch.bits) && lastSeen < ch.round
 }