diff --git a/src/main/java/ru/soune/nocopy/exception/ChunkSizeExceededException.java b/src/main/java/ru/soune/nocopy/exception/ChunkSizeExceededException.java
index a19cd95..f8a4933 100644
--- a/src/main/java/ru/soune/nocopy/exception/ChunkSizeExceededException.java
+++ b/src/main/java/ru/soune/nocopy/exception/ChunkSizeExceededException.java
@@ -2,6 +2,6 @@ package ru.soune.nocopy.exception;
 
 public class ChunkSizeExceededException extends RuntimeException {
     public ChunkSizeExceededException(long actualSize, long maxSize) {
-        super(String.format("Chunk size exceeded: %d > %d", actualSize, maxSize));
+        super(String.format("Chunk size not valid: " + actualSize));
     }
 }
diff --git a/src/main/java/ru/soune/nocopy/service/file/FileEntityService.java b/src/main/java/ru/soune/nocopy/service/file/FileEntityService.java
index 8b239a5..97a6cab 100644
--- a/src/main/java/ru/soune/nocopy/service/file/FileEntityService.java
+++ b/src/main/java/ru/soune/nocopy/service/file/FileEntityService.java
@@ -40,7 +40,6 @@ public class FileEntityService {
 
             long fileSize = Files.size(filePath);
             String originalName = session.getFileName();
-            String extension = extractFileExtension(originalName);
             String storedName = filePath.getFileName().toString();
 
             FileEntity fileEntity = FileEntity.builder()
@@ -50,7 +49,7 @@ public class FileEntityService {
                     .filePath(session.getFilePath())
                     .fileSize(fileSize)
                     .mimeType(session.getFileType())
-                    .fileExtension(extension)
+                    .fileExtension(session.getExtension())
                     .checksum(checksum)
                     .uploadSessionId(session.getUploadId())
                     .status(FileStatus.ACTIVE)
diff --git a/src/main/java/ru/soune/nocopy/service/file/FileUploadServiceImpl.java b/src/main/java/ru/soune/nocopy/service/file/FileUploadServiceImpl.java
index eb48651..93c7d67 100644
--- a/src/main/java/ru/soune/nocopy/service/file/FileUploadServiceImpl.java
+++ b/src/main/java/ru/soune/nocopy/service/file/FileUploadServiceImpl.java
@@ -102,13 +102,14 @@ public class FileUploadServiceImpl implements FileUploadService {
         int totalChunks = (int) Math.ceil((double) fileSize / chunkSize);
         log.debug("File will be split into {} chunks (chunk size: {} bytes)",
                 totalChunks, chunkSize);
+        Long chunkSize = totalChunks == 1 ? fileSize : 5242880L;
 
         FileUploadSession session = FileUploadSession.builder()
                 .userId(userId)
                 .extension(extension)
                 .fileName(fileName)
                 .fileType(fileType)
-                .chunkSize(5242880L)
+                .chunkSize(chunkSize)
                 .fileSize(fileSize)
                 .totalChunks(totalChunks)
                 .chunksUploaded(0)
@@ -148,7 +149,12 @@ public class FileUploadServiceImpl implements FileUploadService {
                             chunkNumber, session.getTotalChunks() - 1));
         }
 
-        if (chunkFile.getSize() > chunkSize) {
+        if (chunkNumber == 0 && chunkFile.getSize() > chunkSize || chunkNumber + 1 == (session.getTotalChunks())
+                && chunkFile.getSize() > chunkSize) {
+            throw new ChunkSizeExceededException(chunkFile.getSize(), chunkSize);
+        }
+
+        if (chunkNumber > 0 && chunkNumber + 1 < session.getTotalChunks() && chunkFile.getSize() != chunkSize) {
             throw new ChunkSizeExceededException(chunkFile.getSize(), chunkSize);
         }
 
@@ -333,36 +339,6 @@ public class FileUploadServiceImpl implements FileUploadService {
         }
     }
 
-//    private void assembleFile(FileUploadSession session) throws IOException {
-//        log.info("Starting file assembly for session: {} ({})",
-//                session.getUploadId(), session.getFileName());
-//
-//        Path finalFilePath = null;
-//
-//        try {
-//            finalFilePath = prepareFinalFile(session);
-//
-//            validateAllChunksExist(session);
-//
-//            mergeChunksToFile(session, finalFilePath);
-//
-//            validateFinalFile(session, finalFilePath);
-//
-//            updateSessionOnSuccess(session, finalFilePath);
-//
-//            cleanupSessionFiles(session);
-//
-//            log.info("File assembly completed: {} -> {} ({} bytes)",
-//                    session.getFileName(), finalFilePath, session.getFileSize());
-//
-//        } catch (Exception e) {
-//            if (finalFilePath != null) {
-//                Files.deleteIfExists(finalFilePath);
-//            }
-//            throw e;
-//        }
-//    }
-
     private void assembleFile(FileUploadSession session) throws IOException {
         log.info("Starting file assembly for session: {} ({})",
                 session.getUploadId(), session.getFileName());