diff --git a/ethereum/spec/src/main/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCache.java b/ethereum/spec/src/main/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCache.java
index 998eb56b59b..98713f69066 100644
--- a/ethereum/spec/src/main/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCache.java
+++ b/ethereum/spec/src/main/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCache.java
@@ -53,14 +53,15 @@ public ValidatorIndexCache() {
 
   public Optional<Integer> getValidatorIndex(
       final BeaconState state, final BLSPublicKey publicKey) {
-    // Store latestFinalizedIndex here in case we need to scan keys from the state.
-    // This ensures we're adding from a point that we're confident the cache is at
-    // when we scan for more keys through the state later.
-    final int latestFinalizedIndexSnapshot = latestFinalizedIndex.get();
     final SszList<Validator> validators = state.getValidators();
-    return validatorIndices
-        .getCached(publicKey)
-        .or(() -> findIndexFromFinalizedState(validators, publicKey, latestFinalizedIndexSnapshot))
+    final Optional<Integer> validatorIndex = validatorIndices.getCached(publicKey);
+    if (validatorIndex.isPresent()) {
+      return validatorIndex.filter(index -> index < validators.size());
+    }
+    // Using the same latestFinalizedIndex when scanning through
+    // the finalized and the non-finalized states ensures consistency
+    final int latestFinalizedIndexSnapshot = latestFinalizedIndex.get();
+    return findIndexFromFinalizedState(validators, publicKey, latestFinalizedIndexSnapshot)
         .or(
             () ->
                 findIndexFromNonFinalizedState(
diff --git a/ethereum/spec/src/test/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCacheTest.java b/ethereum/spec/src/test/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCacheTest.java
index 21da5ab67fc..3e09ce9b3c8 100644
--- a/ethereum/spec/src/test/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCacheTest.java
+++ b/ethereum/spec/src/test/java/tech/pegasys/teku/spec/datastructures/state/beaconstate/common/ValidatorIndexCacheTest.java
@@ -43,6 +43,23 @@ public class ValidatorIndexCacheTest {
   @SuppressWarnings("unchecked")
   final Cache<BLSPublicKey, Integer> cache = mock(Cache.class);
 
+  @Test
+  public void shouldReturnEmptyIfValidatorIndexIsNotConsistentWithNumberOfValidatorsInState() {
+    final SszList<Validator> validators = state.getValidators();
+    final int latestFinalizedIndex = NUMBER_OF_VALIDATORS - 1;
+    final ValidatorIndexCache validatorIndexCache = new ValidatorIndexCache();
+    validatorIndexCache.updateLatestFinalizedIndex(state);
+
+    final BLSPublicKey publicKey = validators.get(latestFinalizedIndex).getPublicKey();
+    // cache eagerly the last validator public key
+    validatorIndexCache.invalidateWithNewValue(publicKey, latestFinalizedIndex);
+
+    // state with one less validator
+    final BeaconState state = dataStructureUtil.randomBeaconState(NUMBER_OF_VALIDATORS - 1);
+
+    assertThat(validatorIndexCache.getValidatorIndex(state, publicKey)).isEmpty();
+  }
+
   @Test
   public void shouldScanFinalizedStateAndCache() {
     final SszList<Validator> validators = state.getValidators();