diff --git a/pkg/sentry/ethereum/services/duties.go b/pkg/sentry/ethereum/services/duties.go
index cf2649fb..d76d5a9c 100644
--- a/pkg/sentry/ethereum/services/duties.go
+++ b/pkg/sentry/ethereum/services/duties.go
@@ -242,7 +242,11 @@ func (m *DutiesService) GetValidatorIndex(epoch phase0.Epoch, slot phase0.Slot,
 			continue
 		}
 
-		return committee.Validators[position], nil
+		if position < uint64(len(committee.Validators)) {
+			return committee.Validators[position], nil
+		} else {
+			return 0, fmt.Errorf("position %d is out of range for slot %d in epoch %d in committee %d", position, slot, epoch, committeeIndex)
+		}
 	}
 
 	return 0, fmt.Errorf("validator index not found")