diff --git a/HISTORY.md b/HISTORY.md
index a6c59d032..9e58ddfaa 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -16,6 +16,7 @@
 * BlobDB no longer updates the SST to blob file mapping upon failed compactions.
 * Fixed a bug where BlobDB was comparing the `ColumnFamilyHandle` pointers themselves instead of only the column family IDs when checking whether an API call uses the default column family or not.
 * Fix a race condition for cfd->log_number_ between manifest switch and memtable switch (PR 6249) when number of column families is greater than 1.
+* Fix a bug on fractional cascading index when multiple files at the same level contain the same smallest user key, and those user keys are for merge operands. In this case, Get() the exact key may miss some merge operands.
 
 ### New Features
 * It is now possible to enable periodic compactions for the base DB when using BlobDB.
diff --git a/db/db_test2.cc b/db/db_test2.cc
index 07ed8608b..07a486186 100644
--- a/db/db_test2.cc
+++ b/db/db_test2.cc
@@ -4266,6 +4266,38 @@ TEST_F(DBTest2, SwitchMemtableRaceWithNewManifest) {
   ASSERT_OK(dbfull()->TEST_WaitForCompact());
   thread.join();
 }
+
+TEST_F(DBTest2, SameSmallestInSameLevel) {
+  // This test validates fractional casacading logic when several files at one
+  // one level only contains the same user key.
+  Options options = CurrentOptions();
+  options.merge_operator = MergeOperators::CreateStringAppendOperator();
+  DestroyAndReopen(options);
+
+  ASSERT_OK(Put("key", "1"));
+  ASSERT_OK(Put("key", "2"));
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "3"));
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "4"));
+  Flush();
+  CompactRangeOptions cro;
+  cro.change_level = true;
+  cro.target_level = 2;
+  ASSERT_OK(dbfull()->CompactRange(cro, db_->DefaultColumnFamily(), nullptr,
+                                   nullptr));
+
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "5"));
+  Flush();
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "6"));
+  Flush();
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "7"));
+  Flush();
+  ASSERT_OK(db_->Merge(WriteOptions(), "key", "8"));
+  Flush();
+  dbfull()->TEST_WaitForCompact(true);
+  ASSERT_EQ("0,4,1", FilesPerLevel());
+
+  ASSERT_EQ("2,3,4,5,6,7,8", Get("key"));
+}
 }  // namespace rocksdb
 
 #ifdef ROCKSDB_UNITTESTS_WITH_CUSTOM_OBJECTS_FROM_STATIC_LIBS
diff --git a/db/file_indexer.cc b/db/file_indexer.cc
index f22211f04..fd0180992 100644
--- a/db/file_indexer.cc
+++ b/db/file_indexer.cc
@@ -157,7 +157,6 @@ void FileIndexer::CalculateLB(
     if (cmp == 0) {
       set_index(&index[upper_idx], lower_idx);
       ++upper_idx;
-      ++lower_idx;
     } else if (cmp > 0) {
       // Lower level's file (largest) is smaller, a key won't hit in that
       // file. Move to next lower file
@@ -195,7 +194,6 @@ void FileIndexer::CalculateRB(
     if (cmp == 0) {
       set_index(&index[upper_idx], lower_idx);
       --upper_idx;
-      --lower_idx;
     } else if (cmp < 0) {
       // Lower level's file (smallest) is larger, a key won't hit in that
       // file. Move to next lower file.