diff --git a/types/validator_set.go b/types/validator_set.go
index 3ec389a48..0e20417a7 100644
--- a/types/validator_set.go
+++ b/types/validator_set.go
@@ -99,7 +99,12 @@ func (valSet *ValidatorSet) GetByAddress(address []byte) (index int, val *Valida
 	}
 }
 
+// GetByIndex returns the validator by index.
+// It returns nil values if index >= len(ValidatorSet.Validators)
 func (valSet *ValidatorSet) GetByIndex(index int) (address []byte, val *Validator) {
+	if index >= len(valSet.Validators) {
+		return nil, nil
+	}
 	val = valSet.Validators[index]
 	return val.Address, val.Copy()
 }
diff --git a/types/vote.go b/types/vote.go
index 164293c53..658415682 100644
--- a/types/vote.go
+++ b/types/vote.go
@@ -13,9 +13,9 @@ import (
 
 var (
 	ErrVoteUnexpectedStep          = errors.New("Unexpected step")
-	ErrVoteInvalidValidatorIndex   = errors.New("Invalid round vote validator index")
-	ErrVoteInvalidValidatorAddress = errors.New("Invalid round vote validator address")
-	ErrVoteInvalidSignature        = errors.New("Invalid round vote signature")
+	ErrVoteInvalidValidatorIndex   = errors.New("Invalid validator index")
+	ErrVoteInvalidValidatorAddress = errors.New("Invalid validator address")
+	ErrVoteInvalidSignature        = errors.New("Invalid signature")
 	ErrVoteInvalidBlockHash        = errors.New("Invalid block hash")
 )
 
diff --git a/types/vote_set.go b/types/vote_set.go
index 938dbcb61..7a5d52671 100644
--- a/types/vote_set.go
+++ b/types/vote_set.go
@@ -140,8 +140,10 @@ func (voteSet *VoteSet) addVote(vote *Vote) (added bool, err error) {
 	blockKey := vote.BlockID.Key()
 
 	// Ensure that validator index was set
-	if valIndex < 0 || len(valAddr) == 0 {
-		panic("Validator index or address was not set in vote.")
+	if valIndex < 0 {
+		return false, ErrVoteInvalidValidatorIndex
+	} else if len(valAddr) == 0 {
+		return false, ErrVoteInvalidValidatorAddress
 	}
 
 	// Make sure the step matches.