diff --git a/fs_mgr/libsnapshot/cow_reader.cpp b/fs_mgr/libsnapshot/cow_reader.cpp
index e8f0153..5306b28 100644
--- a/fs_mgr/libsnapshot/cow_reader.cpp
+++ b/fs_mgr/libsnapshot/cow_reader.cpp
@@ -231,7 +231,7 @@
                 memcpy(&footer_->op, &current_op, sizeof(footer->op));
                 off_t offs = lseek(fd_.get(), pos, SEEK_SET);
                 if (offs < 0 || pos != static_cast<uint64_t>(offs)) {
-                    PLOG(ERROR) << "lseek next op failed";
+                    PLOG(ERROR) << "lseek next op failed " << offs;
                     return false;
                 }
                 if (!android::base::ReadFully(fd_, &footer->data, sizeof(footer->data))) {
@@ -251,7 +251,7 @@
         // Position for next cluster read
         off_t offs = lseek(fd_.get(), pos, SEEK_SET);
         if (offs < 0 || pos != static_cast<uint64_t>(offs)) {
-            PLOG(ERROR) << "lseek next op failed";
+            PLOG(ERROR) << "lseek next op failed " << offs;
             return false;
         }
         ops_buffer->resize(current_op_num);
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_writer.h
index 3655c01..b0be5a5 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_writer.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/mock_snapshot_writer.h
@@ -44,6 +44,7 @@
 
     // Open the writer in write mode (no append).
     MOCK_METHOD(bool, Initialize, (), (override));
+    MOCK_METHOD(bool, VerifyMergeOps, (), (override, const, noexcept));
 
     // Open the writer in append mode, with the last label to resume
     // from. See CowWriter::InitializeAppend.
diff --git a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_writer.h b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_writer.h
index b09e1ae..545f117 100644
--- a/fs_mgr/libsnapshot/include/libsnapshot/snapshot_writer.h
+++ b/fs_mgr/libsnapshot/include/libsnapshot/snapshot_writer.h
@@ -47,6 +47,7 @@
     virtual bool InitializeAppend(uint64_t label) = 0;
 
     virtual std::unique_ptr<FileDescriptor> OpenReader() = 0;
+    virtual bool VerifyMergeOps() const noexcept = 0;
 
   protected:
     android::base::borrowed_fd GetSourceFd();
@@ -58,7 +59,7 @@
 };
 
 // Send writes to a COW or a raw device directly, based on a threshold.
-class CompressedSnapshotWriter : public ISnapshotWriter {
+class CompressedSnapshotWriter final : public ISnapshotWriter {
   public:
     CompressedSnapshotWriter(const CowOptions& options);
 
@@ -70,6 +71,7 @@
     bool Finalize() override;
     uint64_t GetCowSize() override;
     std::unique_ptr<FileDescriptor> OpenReader() override;
+    bool VerifyMergeOps() const noexcept;
 
   protected:
     bool EmitCopy(uint64_t new_block, uint64_t old_block) override;
@@ -81,13 +83,14 @@
     bool EmitSequenceData(size_t num_ops, const uint32_t* data) override;
 
   private:
+    std::unique_ptr<CowReader> OpenCowReader() const;
     android::base::unique_fd cow_device_;
 
     std::unique_ptr<CowWriter> cow_;
 };
 
 // Write directly to a dm-snapshot device.
-class OnlineKernelSnapshotWriter : public ISnapshotWriter {
+class OnlineKernelSnapshotWriter final : public ISnapshotWriter {
   public:
     OnlineKernelSnapshotWriter(const CowOptions& options);
 
@@ -101,6 +104,10 @@
     uint64_t GetCowSize() override { return cow_size_; }
     std::unique_ptr<FileDescriptor> OpenReader() override;
 
+    // Online kernel snapshot writer doesn't care about merge sequences.
+    // So ignore.
+    bool VerifyMergeOps() const noexcept override { return true; }
+
   protected:
     bool EmitRawBlocks(uint64_t new_block_start, const void* data, size_t size) override;
     bool EmitZeroBlocks(uint64_t new_block_start, uint64_t num_blocks) override;
diff --git a/fs_mgr/libsnapshot/snapshot_writer.cpp b/fs_mgr/libsnapshot/snapshot_writer.cpp
index 3eda08e..48b7d80 100644
--- a/fs_mgr/libsnapshot/snapshot_writer.cpp
+++ b/fs_mgr/libsnapshot/snapshot_writer.cpp
@@ -67,7 +67,7 @@
     return cow_->GetCowSize();
 }
 
-std::unique_ptr<FileDescriptor> CompressedSnapshotWriter::OpenReader() {
+std::unique_ptr<CowReader> CompressedSnapshotWriter::OpenCowReader() const {
     unique_fd cow_fd(dup(cow_device_.get()));
     if (cow_fd < 0) {
         PLOG(ERROR) << "dup COW device";
@@ -79,6 +79,20 @@
         LOG(ERROR) << "Unable to read COW";
         return nullptr;
     }
+    return cow;
+}
+
+bool CompressedSnapshotWriter::VerifyMergeOps() const noexcept {
+    auto cow_reader = OpenCowReader();
+    if (cow_reader == nullptr) {
+        LOG(ERROR) << "Couldn't open CowReader";
+        return false;
+    }
+    return cow_reader->VerifyMergeOps();
+}
+
+std::unique_ptr<FileDescriptor> CompressedSnapshotWriter::OpenReader() {
+    auto cow = OpenCowReader();
 
     auto reader = std::make_unique<CompressedSnapshotReader>();
     if (!reader->SetCow(std::move(cow))) {