diff --git a/error.go b/error.go
index 9e2bf6d..6c76313 100644
--- a/error.go
+++ b/error.go
@@ -19,4 +19,6 @@ var (
 	ErrCantFindDraftRevision                 = errors.New("can't find a draft revision")
 	ErrWrongUsageOfGetLinkKR                 = errors.New("internal error for GetLinkKR - nil passed in for link")
 	ErrWrongUsageOfGetLink                   = errors.New("internal error for getLink - empty linkID passed in")
+	ErrFileEncryptionReturnDataMissing       = errors.New("internal error for file upload - encRetChan returns nil")
+	ErrFileEncryptionMissingIndex            = errors.New("internal error for file upload - data from encRetChan is missing an index")
 )
diff --git a/file.go b/file.go
index 5481cc6..e96b6d6 100644
--- a/file.go
+++ b/file.go
@@ -456,7 +456,7 @@ func (protonDrive *ProtonDrive) createFileUploadDraft(ctx context.Context, paren
 }
 
 func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, newSessionKey *crypto.SessionKey, newNodeKR *crypto.KeyRing, file io.Reader, linkID, revisionID string) ([]byte, int64, error) {
-	type PendingUploadBlocks struct {
+	type PendingUploadBlock struct {
 		blockUploadInfo proton.BlockUploadInfo
 		encData         []byte
 	}
@@ -467,7 +467,7 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 
 	totalFileSize := int64(0)
 
-	pendingUploadBlocks := make([]PendingUploadBlocks, 0)
+	pendingUploadBlocks := make([]*PendingUploadBlock, 0)
 	manifestSignatureData := make([]byte, 0)
 	uploadPendingBlocks := func() error {
 		if len(pendingUploadBlocks) == 0 {
@@ -491,24 +491,21 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 			return err
 		}
 
-		errChan := make(chan error)
-		uploadBlockWrapper := func(ctx context.Context, errChan chan error, bareURL, token string, block io.Reader) {
-			// log.Println("Before semaphore")
+		uploadErrChan := make(chan error)
+		uploadBlockWrapper := func(ctx context.Context, uploadErrChan chan error, bareURL, token string, block io.Reader) {
 			if err := protonDrive.blockUploadSemaphore.Acquire(ctx, 1); err != nil {
-				errChan <- err
+				uploadErrChan <- err
 			}
 			defer protonDrive.blockUploadSemaphore.Release(1)
-			// log.Println("After semaphore")
-			// defer log.Println("Release semaphore")
 
-			errChan <- protonDrive.c.UploadBlock(ctx, bareURL, token, block)
+			uploadErrChan <- protonDrive.c.UploadBlock(ctx, bareURL, token, block)
 		}
 		for i := range blockUploadResp {
-			go uploadBlockWrapper(ctx, errChan, blockUploadResp[i].BareURL, blockUploadResp[i].Token, bytes.NewReader(pendingUploadBlocks[i].encData))
+			go uploadBlockWrapper(ctx, uploadErrChan, blockUploadResp[i].BareURL, blockUploadResp[i].Token, bytes.NewReader(pendingUploadBlocks[i].encData))
 		}
 
 		for i := 0; i < len(blockUploadResp); i++ {
-			err := <-errChan
+			err := <-uploadErrChan
 			if err != nil {
 				return err
 			}
@@ -519,11 +516,109 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 		return nil
 	}
 
+	type encChanData struct {
+		hash         []byte
+		pendingBlock *PendingUploadBlock
+		err          error
+	}
+	encryptDataBlock := func(encRetChan chan *encChanData, ctx context.Context, idx int, data []byte) {
+		if err := protonDrive.blockCryptoSemaphore.Acquire(ctx, 1); err != nil {
+			encRetChan <- &encChanData{
+				err: err,
+			}
+		}
+		defer protonDrive.blockCryptoSemaphore.Release(1)
+
+		// encrypt data
+		dataPlainMessage := crypto.NewPlainMessage(data)
+		encData, err := newSessionKey.Encrypt(dataPlainMessage)
+		if err != nil {
+			encRetChan <- &encChanData{
+				err: err,
+			}
+		}
+
+		encSignature, err := protonDrive.AddrKR.SignDetachedEncrypted(dataPlainMessage, newNodeKR)
+		if err != nil {
+			encRetChan <- &encChanData{
+				err: err,
+			}
+		}
+		encSignatureStr, err := encSignature.GetArmored()
+		if err != nil {
+			encRetChan <- &encChanData{
+				err: err,
+			}
+		}
+
+		h := sha256.New()
+		h.Write(encData)
+		hash := h.Sum(nil)
+		base64Hash := base64.StdEncoding.EncodeToString(hash)
+		if err != nil {
+			encRetChan <- &encChanData{
+				err: err,
+			}
+		}
+
+		encRetChan <- &encChanData{
+			hash: hash,
+			pendingBlock: &PendingUploadBlock{
+				blockUploadInfo: proton.BlockUploadInfo{
+					Index:        idx, // iOS drive: BE starts with 1
+					Size:         int64(len(encData)),
+					EncSignature: encSignatureStr,
+					Hash:         base64Hash,
+				},
+				encData: encData,
+			},
+			err: nil,
+		}
+	}
+
+	checkAndUploadPendingBlocks := func(encRetChan chan *encChanData, nextIndex, pendingBlocks *int) error {
+		cacheEncChanData := make(map[int]*encChanData)
+		for i := 0; i < *pendingBlocks; i++ {
+			tmp := <-encRetChan
+
+			if tmp.err != nil {
+				return tmp.err
+			}
+
+			if tmp == nil {
+				return ErrFileEncryptionReturnDataMissing
+			}
+			cacheEncChanData[tmp.pendingBlock.blockUploadInfo.Index] = tmp
+		}
+
+		for i := 0; i < len(cacheEncChanData); i++ {
+			if val, ok := cacheEncChanData[*nextIndex]; ok {
+				manifestSignatureData = append(manifestSignatureData, val.hash...)
+
+				pendingUploadBlocks = append(pendingUploadBlocks, val.pendingBlock)
+			} else {
+				return ErrFileEncryptionMissingIndex
+			}
+
+			*nextIndex++
+		}
+
+		err := uploadPendingBlocks()
+		if err != nil {
+			return err
+		}
+
+		*pendingBlocks = 0
+		return nil
+	}
+
 	shouldContinue := true
+	encRetChan := make(chan *encChanData)
+	nextIdx := 1
+	pendingBlocks := 0
 	for i := 1; shouldContinue; i++ {
 		if (i-1) > 0 && (i-1)%UPLOAD_BATCH_BLOCK_SIZE == 0 {
-			err := uploadPendingBlocks()
-			if err != nil {
+			if err := checkAndUploadPendingBlocks(encRetChan, &nextIdx, &pendingBlocks); err != nil {
 				return nil, 0, err
 			}
 		}
@@ -547,43 +642,10 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 		data = data[:readBytes]
 		totalFileSize += int64(readBytes)
 
-		// encrypt data
-		dataPlainMessage := crypto.NewPlainMessage(data)
-		encData, err := newSessionKey.Encrypt(dataPlainMessage)
-		if err != nil {
-			return nil, 0, err
-		}
-
-		encSignature, err := protonDrive.AddrKR.SignDetachedEncrypted(dataPlainMessage, newNodeKR)
-		if err != nil {
-			return nil, 0, err
-		}
-		encSignatureStr, err := encSignature.GetArmored()
-		if err != nil {
-			return nil, 0, err
-		}
-
-		h := sha256.New()
-		h.Write(encData)
-		hash := h.Sum(nil)
-		base64Hash := base64.StdEncoding.EncodeToString(hash)
-		if err != nil {
-			return nil, 0, err
-		}
-		manifestSignatureData = append(manifestSignatureData, hash...)
-
-		pendingUploadBlocks = append(pendingUploadBlocks, PendingUploadBlocks{
-			blockUploadInfo: proton.BlockUploadInfo{
-				Index:        i, // iOS drive: BE starts with 1
-				Size:         int64(len(encData)),
-				EncSignature: encSignatureStr,
-				Hash:         base64Hash,
-			},
-			encData: encData,
-		})
+		pendingBlocks += 1
+		go encryptDataBlock(encRetChan, ctx, i, data)
 	}
-	err := uploadPendingBlocks()
-	if err != nil {
+	if err := checkAndUploadPendingBlocks(encRetChan, &nextIdx, &pendingBlocks); err != nil {
 		return nil, 0, err
 	}