diff --git a/src/bucket/BucketOutputIterator.cpp b/src/bucket/BucketOutputIterator.cpp
index 6645f51143..43fd611cd9 100644
--- a/src/bucket/BucketOutputIterator.cpp
+++ b/src/bucket/BucketOutputIterator.cpp
@@ -168,7 +168,8 @@ template <typename BucketT>
 std::shared_ptr<BucketT>
 BucketOutputIterator<BucketT>::getBucket(
     BucketManager& bucketManager, MergeKey* mergeKey,
-    std::unique_ptr<std::vector<typename BucketT::EntryT>> inMemoryState)
+    std::unique_ptr<std::vector<typename BucketT::EntryT>> inMemoryState,
+    std::shared_ptr<typename BucketT::IndexT const> preBuiltIndex)
 {
     ZoneScoped;
     if (mBuf)
@@ -219,7 +220,11 @@ BucketOutputIterator<BucketT>::getBucket(
 
     if (!index)
     {
-        if constexpr (std::is_same_v<BucketT, LiveBucket>)
+        if (preBuiltIndex)
+        {
+            index = std::move(preBuiltIndex);
+        }
+        else if constexpr (std::is_same_v<BucketT, LiveBucket>)
         {
             if (inMemoryState)
             {
diff --git a/src/bucket/BucketOutputIterator.h b/src/bucket/BucketOutputIterator.h
index a76e1c6bb7..99b42ec2d0 100644
--- a/src/bucket/BucketOutputIterator.h
+++ b/src/bucket/BucketOutputIterator.h
@@ -55,6 +55,8 @@ template <typename BucketT> class BucketOutputIterator
     std::shared_ptr<BucketT> getBucket(
         BucketManager& bucketManager, MergeKey* mergeKey = nullptr,
         std::unique_ptr<std::vector<typename BucketT::EntryT>> inMemoryState =
+            nullptr,
+        std::shared_ptr<typename BucketT::IndexT const> preBuiltIndex =
             nullptr);
 };
 }
diff --git a/src/bucket/LiveBucket.cpp b/src/bucket/LiveBucket.cpp
index 8101c9d183..e38287636b 100644
--- a/src/bucket/LiveBucket.cpp
+++ b/src/bucket/LiveBucket.cpp
@@ -10,6 +10,7 @@
 #include "bucket/BucketOutputIterator.h"
 #include "bucket/BucketUtils.h"
 #include "bucket/LedgerCmp.h"
+#include <future>
 #include <medida/counter.h>
 
 namespace stellar
@@ -595,6 +596,14 @@ LiveBucket::mergeInMemory(BucketManager& bucketManager,
         bucketManager.incrMergeCounters<LiveBucket>(mc);
     }
 
+    // Start index construction on a worker thread, the inputs are all
+    // read-only from that point on.
+    auto indexFuture = std::async(
+        std::launch::async, [&bucketManager, &mergedEntries, &meta]() {
+            return std::make_shared<LiveBucketIndex const>(bucketManager,
+                                                           mergedEntries, meta);
+        });
+
     // Write merge output to a bucket and save to disk
     LiveBucketOutputIterator out(bucketManager.getTmpDir(),
                                  /*keepTombstoneEntries=*/true, meta, mc, ctx,
@@ -605,11 +614,14 @@ LiveBucket::mergeInMemory(BucketManager& bucketManager,
         out.put(e);
     }
 
+    auto preBuiltIndex = indexFuture.get();
+
     // Store the merged entries in memory in the new bucket in case this
     // bucket sees another incoming merge as level 0 curr.
     return out.getBucket(
         bucketManager, nullptr,
-        std::make_unique<std::vector<BucketEntry>>(std::move(mergedEntries)));
+        std::make_unique<std::vector<BucketEntry>>(std::move(mergedEntries)),
+        std::move(preBuiltIndex));
 }
 
 BucketEntryCounters const&