diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
index a0c5c6658..febb4847d 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/merge_worker.cpp
@@ -233,6 +233,11 @@ bool MergeWorker::MergeOrderedOpsAsync() {
             return false;
         }
 
+        std::optional<std::lock_guard<std::mutex>> buffer_lock;
+        // Acquire the buffer lock at this point so that RA thread
+        // doesn't step into this buffer. See b/377819507
+        buffer_lock.emplace(snapuserd_->GetBufferLock());
+
         snapuserd_->SetMergeInProgress(ra_block_index_);
 
         loff_t offset = 0;
@@ -383,6 +388,9 @@ bool MergeWorker::MergeOrderedOpsAsync() {
         // Mark the block as merge complete
         snapuserd_->SetMergeCompleted(ra_block_index_);
 
+        // Release the buffer lock
+        buffer_lock.reset();
+
         // Notify RA thread that the merge thread is ready to merge the next
         // window
         snapuserd_->NotifyRAForMergeReady();
@@ -415,6 +423,11 @@ bool MergeWorker::MergeOrderedOps() {
             return false;
         }
 
+        std::optional<std::lock_guard<std::mutex>> buffer_lock;
+        // Acquire the buffer lock at this point so that RA thread
+        // doesn't step into this buffer. See b/377819507
+        buffer_lock.emplace(snapuserd_->GetBufferLock());
+
         snapuserd_->SetMergeInProgress(ra_block_index_);
 
         loff_t offset = 0;
@@ -468,6 +481,9 @@ bool MergeWorker::MergeOrderedOps() {
         // Mark the block as merge complete
         snapuserd_->SetMergeCompleted(ra_block_index_);
 
+        // Release the buffer lock
+        buffer_lock.reset();
+
         // Notify RA thread that the merge thread is ready to merge the next
         // window
         snapuserd_->NotifyRAForMergeReady();
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_core.h b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_core.h
index c7de9951f..2340b0b20 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_core.h
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_core.h
@@ -186,6 +186,7 @@ class SnapshotHandler : public std::enable_shared_from_this<SnapshotHandler> {
 
     bool IsIouringSupported();
     bool CheckPartitionVerification();
+    std::mutex& GetBufferLock() { return buffer_lock_; }
 
   private:
     bool ReadMetadata();
@@ -216,6 +217,9 @@ class SnapshotHandler : public std::enable_shared_from_this<SnapshotHandler> {
     std::mutex lock_;
     std::condition_variable cv;
 
+    // Lock the buffer used for snapshot-merge
+    std::mutex buffer_lock_;
+
     void* mapped_addr_;
     size_t total_mapped_addr_length_;
 
diff --git a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
index 3007d45f4..c7ae51926 100644
--- a/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
+++ b/fs_mgr/libsnapshot/snapuserd/user-space-merge/snapuserd_readahead.cpp
@@ -706,25 +706,32 @@ bool ReadAhead::ReadAheadIOStart() {
         return false;
     }
 
-    // Copy the data to scratch space
-    memcpy(metadata_buffer_, ra_temp_meta_buffer_.get(), snapuserd_->GetBufferMetadataSize());
-    memcpy(read_ahead_buffer_, ra_temp_buffer_.get(), total_blocks_merged_ * BLOCK_SZ);
+    // Acquire buffer lock before doing memcpy to the scratch buffer. Although,
+    // by now snapshot-merge thread shouldn't be working on this scratch space
+    // but we take additional measure to ensure that the buffer is not being
+    // used by the merge thread at this point. see b/377819507
+    {
+        std::lock_guard<std::mutex> buffer_lock(snapuserd_->GetBufferLock());
+        // Copy the data to scratch space
+        memcpy(metadata_buffer_, ra_temp_meta_buffer_.get(), snapuserd_->GetBufferMetadataSize());
+        memcpy(read_ahead_buffer_, ra_temp_buffer_.get(), total_blocks_merged_ * BLOCK_SZ);
 
-    loff_t offset = 0;
-    std::unordered_map<uint64_t, void*>& read_ahead_buffer_map = snapuserd_->GetReadAheadMap();
-    read_ahead_buffer_map.clear();
+        loff_t offset = 0;
+        std::unordered_map<uint64_t, void*>& read_ahead_buffer_map = snapuserd_->GetReadAheadMap();
+        read_ahead_buffer_map.clear();
 
-    for (size_t block_index = 0; block_index < blocks_.size(); block_index++) {
-        void* bufptr = static_cast<void*>((char*)read_ahead_buffer_ + offset);
-        uint64_t new_block = blocks_[block_index];
+        for (size_t block_index = 0; block_index < blocks_.size(); block_index++) {
+            void* bufptr = static_cast<void*>((char*)read_ahead_buffer_ + offset);
+            uint64_t new_block = blocks_[block_index];
 
-        read_ahead_buffer_map[new_block] = bufptr;
-        offset += BLOCK_SZ;
+            read_ahead_buffer_map[new_block] = bufptr;
+            offset += BLOCK_SZ;
+        }
+
+        total_ra_blocks_completed_ += total_blocks_merged_;
+        snapuserd_->SetMergedBlockCountForNextCommit(total_blocks_merged_);
     }
 
-    total_ra_blocks_completed_ += total_blocks_merged_;
-    snapuserd_->SetMergedBlockCountForNextCommit(total_blocks_merged_);
-
     // Flush the scratch data - Technically, we should flush only for overlapping
     // blocks; However, since this region is mmap'ed, the dirty pages can still
     // get flushed to disk at any random point in time. Instead, make sure