diff --git a/beacon/validator/src/main/java/tech/pegasys/teku/validator/coordinator/publisher/AbstractBlockPublisher.java b/beacon/validator/src/main/java/tech/pegasys/teku/validator/coordinator/publisher/AbstractBlockPublisher.java
index 922bb8f7efd..a64f7e262e9 100644
--- a/beacon/validator/src/main/java/tech/pegasys/teku/validator/coordinator/publisher/AbstractBlockPublisher.java
+++ b/beacon/validator/src/main/java/tech/pegasys/teku/validator/coordinator/publisher/AbstractBlockPublisher.java
@@ -61,7 +61,7 @@ public SafeFuture<SendSignedBlockResult> sendSignedBlock(
         .thenCompose(
             signedBlock -> {
               // creating blob sidecars after unblinding the block to ensure in the blinded flow we
-              // already have cached the builder payload
+              // will have the cached builder payload
               final List<BlobSidecar> blobSidecars =
                   blockFactory.createBlobSidecars(blockContainer);
               return gossipAndImportUnblindedSignedBlockAndBlobSidecars(
diff --git a/ethereum/spec/src/testFixtures/java/tech/pegasys/teku/spec/util/DataStructureUtil.java b/ethereum/spec/src/testFixtures/java/tech/pegasys/teku/spec/util/DataStructureUtil.java
index 71dbef4bbcf..d7a49cb3dbc 100644
--- a/ethereum/spec/src/testFixtures/java/tech/pegasys/teku/spec/util/DataStructureUtil.java
+++ b/ethereum/spec/src/testFixtures/java/tech/pegasys/teku/spec/util/DataStructureUtil.java
@@ -2561,7 +2561,7 @@ public BlobSidecar build() {
               .getBlobSidecarSchema();
 
       return blobSidecarSchema.create(
-          index.orElse(randomUInt64()),
+          index.orElse(randomBlobSidecarIndex()),
           blob.orElse(randomBytes(blobSidecarSchema.getBlobSchema().getLength())),
           kzgCommitment.orElse(randomBytes48()),
           kzgProof.orElse(randomBytes48()),
@@ -2612,6 +2612,10 @@ public RewardAndPenaltyDeltas randomRewardAndPenaltyDeltas(final int validatorCo
     return rewardAndPenaltyDeltas;
   }
 
+  private UInt64 randomBlobSidecarIndex() {
+    return randomUInt64(spec.getMaxBlobsPerBlock().orElseThrow());
+  }
+
   private int randomNumberOfBlobsPerBlock() {
     // minimum 1 blob
     return randomInt(1, spec.getMaxBlobsPerBlock().orElseThrow() + 1);