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();