diff --git a/db/compaction/compaction.cc b/db/compaction/compaction.cc
index 9dffb08991..81bdcbe7a0 100644
--- a/db/compaction/compaction.cc
+++ b/db/compaction/compaction.cc
@@ -342,6 +342,8 @@ bool Compaction::SupportsPerKeyPlacement() const {
 
 int Compaction::GetPenultimateLevel() const { return penultimate_level_; }
 
+// smallest_key and largest_key include timestamps if user-defined timestamp is
+// enabled.
 bool Compaction::OverlapPenultimateLevelOutputRange(
     const Slice& smallest_key, const Slice& largest_key) const {
   if (!SupportsPerKeyPlacement()) {
@@ -350,11 +352,13 @@ bool Compaction::OverlapPenultimateLevelOutputRange(
   const Comparator* ucmp =
       input_vstorage_->InternalComparator()->user_comparator();
 
-  return ucmp->Compare(smallest_key, penultimate_level_largest_user_key_) <=
-             0 &&
-         ucmp->Compare(largest_key, penultimate_level_smallest_user_key_) >= 0;
+  return ucmp->CompareWithoutTimestamp(
+             smallest_key, penultimate_level_largest_user_key_) <= 0 &&
+         ucmp->CompareWithoutTimestamp(
+             largest_key, penultimate_level_smallest_user_key_) >= 0;
 }
 
+// key includes timestamp if user-defined timestamp is enabled.
 bool Compaction::WithinPenultimateLevelOutputRange(const Slice& key) const {
   if (!SupportsPerKeyPlacement()) {
     return false;
@@ -363,8 +367,10 @@ bool Compaction::WithinPenultimateLevelOutputRange(const Slice& key) const {
   const Comparator* ucmp =
       input_vstorage_->InternalComparator()->user_comparator();
 
-  return ucmp->Compare(key, penultimate_level_smallest_user_key_) >= 0 &&
-         ucmp->Compare(key, penultimate_level_largest_user_key_) <= 0;
+  return ucmp->CompareWithoutTimestamp(
+             key, penultimate_level_smallest_user_key_) >= 0 &&
+         ucmp->CompareWithoutTimestamp(
+             key, penultimate_level_largest_user_key_) <= 0;
 }
 
 bool Compaction::InputCompressionMatchesOutput() const {
diff --git a/db/compaction/compaction.h b/db/compaction/compaction.h
index 22c30c9c34..b073ed61dd 100644
--- a/db/compaction/compaction.h
+++ b/db/compaction/compaction.h
@@ -319,6 +319,8 @@ class Compaction {
 
   // Return true if the given range is overlap with penultimate level output
   // range.
+  // Both smallest_key and largest_key include timestamps if user-defined
+  // timestamp is enabled.
   bool OverlapPenultimateLevelOutputRange(const Slice& smallest_key,
                                           const Slice& largest_key) const;
 
@@ -328,6 +330,7 @@ class Compaction {
   // If per_key_placement is not supported, always return false.
   // TODO: currently it doesn't support moving data from the last level to the
   //  penultimate level
+  //  key includes timestamp if user-defined timestamp is enabled.
   bool WithinPenultimateLevelOutputRange(const Slice& key) const;
 
   CompactionReason compaction_reason() const { return compaction_reason_; }
@@ -474,9 +477,11 @@ class Compaction {
   TablePropertiesCollection output_table_properties_;
 
   // smallest user keys in compaction
+  // includes timestamp if user-defined timestamp is enabled.
   Slice smallest_user_key_;
 
   // largest user keys in compaction
+  // includes timestamp if user-defined timestamp is enabled.
   Slice largest_user_key_;
 
   // Reason for compaction
@@ -497,6 +502,7 @@ class Compaction {
   const int penultimate_level_;
 
   // Key range for penultimate level output
+  // includes timestamp if user-defined timestamp is enabled.
   Slice penultimate_level_smallest_user_key_;
   Slice penultimate_level_largest_user_key_;
 };
diff --git a/db/compaction/compaction_iterator.h b/db/compaction/compaction_iterator.h
index c337f76e03..c5b7b67bd8 100644
--- a/db/compaction/compaction_iterator.h
+++ b/db/compaction/compaction_iterator.h
@@ -88,6 +88,7 @@ class CompactionIterator {
 
     virtual int number_levels() const = 0;
 
+    // Result includes timestamp if user-defined timestamp is enabled.
     virtual Slice GetLargestUserKey() const = 0;
 
     virtual bool allow_ingest_behind() const = 0;
@@ -108,6 +109,7 @@ class CompactionIterator {
 
     virtual bool SupportsPerKeyPlacement() const = 0;
 
+    // `key` includes timestamp if user-defined timestamp is enabled.
     virtual bool WithinPenultimateLevelOutputRange(const Slice& key) const = 0;
   };
 
@@ -133,6 +135,7 @@ class CompactionIterator {
 
     int number_levels() const override { return compaction_->number_levels(); }
 
+    // Result includes timestamp if user-defined timestamp is enabled.
     Slice GetLargestUserKey() const override {
       return compaction_->GetLargestUserKey();
     }
@@ -173,6 +176,7 @@ class CompactionIterator {
 
     // Check if key is within penultimate level output range, to see if it's
     // safe to output to the penultimate level for per_key_placement feature.
+    // `key` includes timestamp if user-defined timestamp is enabled.
     bool WithinPenultimateLevelOutputRange(const Slice& key) const override {
       return compaction_->WithinPenultimateLevelOutputRange(key);
     }