diff --git a/beacon-chain/core/epoch/precompute/reward_penalty.go b/beacon-chain/core/epoch/precompute/reward_penalty.go
index 07868da4f..8e1e108fd 100644
--- a/beacon-chain/core/epoch/precompute/reward_penalty.go
+++ b/beacon-chain/core/epoch/precompute/reward_penalty.go
@@ -162,7 +162,7 @@ func ProposersDelta(state *stateTrie.BeaconState, pBal *Balance, vp []*Validator
 	baseRewardsPerEpoch := params.BeaconConfig().BaseRewardsPerEpoch
 	proposerRewardQuotient := params.BeaconConfig().ProposerRewardQuotient
 	for _, v := range vp {
-		if v.ProposerIndex > uint64(len(rewards)) {
+		if v.ProposerIndex >= uint64(len(rewards)) {
 			// This should never happen with a valid state / validator.
 			return nil, errors.New("proposer index out of range")
 		}
diff --git a/beacon-chain/core/epoch/precompute/reward_penalty_test.go b/beacon-chain/core/epoch/precompute/reward_penalty_test.go
index 3df1ddddb..726263e77 100644
--- a/beacon-chain/core/epoch/precompute/reward_penalty_test.go
+++ b/beacon-chain/core/epoch/precompute/reward_penalty_test.go
@@ -368,7 +368,7 @@ func TestProposerDeltaPrecompute_ValidatorIndexOutOfRange(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	proposerIndex := validatorCount + 1
+	proposerIndex := validatorCount
 	b := &Balance{ActiveCurrentEpoch: 1000}
 	v := []*Validator{
 		{IsPrevEpochAttester: true, CurrentEpochEffectiveBalance: 32, ProposerIndex: proposerIndex},