diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 10ae6974..c4378960 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -53,7 +53,7 @@ jobs:
         with:
           go-version: ${{ env.GO_VERSION }}
       - name: Run Unit tests.
-        run: go test $(go list ./... | grep -v /cmd/ | grep -v /bind/ ) -v -covermode=count -coverprofile=coverage.txt
+        run: go test $(go list ./... | grep -v /cmd/ | grep -v /bind/) -v -covermode=count -coverprofile=coverage.txt
       - uses: codecov/codecov-action@v4
         with:
           files: ./coverage.txt
diff --git a/internal/protocol/http/fetcher.go b/internal/protocol/http/fetcher.go
index 3c5e34a3..73e43c2a 100644
--- a/internal/protocol/http/fetcher.go
+++ b/internal/protocol/http/fetcher.go
@@ -51,6 +51,11 @@ type chunk struct {
 	retryTimes int
 }
 
+// get remain to download bytes
+func (c *chunk) remain() int64 {
+	return c.End - c.Begin + 1 - c.Downloaded
+}
+
 func newChunk(begin int64, end int64) *chunk {
 	return &chunk{
 		Begin: begin,
@@ -319,7 +324,7 @@ func (f *Fetcher) fetchChunk(index int, ctx context.Context) (err error) {
 	// retry until all remain chunks failed
 	for {
 		// if chunk is completed, return
-		if f.meta.Res.Range && chunk.Downloaded >= chunk.End-chunk.Begin+1 {
+		if f.meta.Res.Range && chunk.remain() <= 0 {
 			return nil
 		}
 		// if all chunks failed, return
@@ -364,15 +369,30 @@ func (f *Fetcher) fetchChunk(index int, ctx context.Context) (err error) {
 				err = NewRequestError(resp.StatusCode, resp.Status)
 				return err
 			}
+			chunk.failed = false
 			reader := NewTimeoutReader(resp.Body, readTimeout)
 			for {
 				n, err := reader.Read(buf)
 				if n > 0 {
+					finished := false
+					if f.meta.Res.Range {
+						remain := chunk.remain()
+						// If downloaded bytes exceed the remain bytes, only write remain bytes
+						if remain < int64(n) {
+							n = int(remain)
+							finished = true
+						}
+					}
+
 					_, err := f.file.WriteAt(buf[:n], chunk.Begin+chunk.Downloaded)
 					if err != nil {
 						return err
 					}
 					chunk.Downloaded += int64(n)
+
+					if finished {
+						return nil
+					}
 				}
 				if err != nil {
 					if err == io.EOF {
diff --git a/internal/protocol/http/fetcher_test.go b/internal/protocol/http/fetcher_test.go
index e8673c55..89a43d4b 100644
--- a/internal/protocol/http/fetcher_test.go
+++ b/internal/protocol/http/fetcher_test.go
@@ -176,6 +176,14 @@ func TestFetcher_DownloadResponseBodyReadTimeout(t *testing.T) {
 	downloadError(listener, 4, t)
 }
 
+func TestFetcher_DownloadOnBugFileServer(t *testing.T) {
+	listener := test.StartTestRangeBugServer()
+	defer listener.Close()
+
+	downloadNormal(listener, 1, t)
+	downloadNormal(listener, 4, t)
+}
+
 func TestFetcher_DownloadResume(t *testing.T) {
 	listener := test.StartTestFileServer()
 	defer listener.Close()
diff --git a/internal/test/httptest.go b/internal/test/httptest.go
index 85696748..54dec46e 100644
--- a/internal/test/httptest.go
+++ b/internal/test/httptest.go
@@ -180,68 +180,98 @@ func StartTestLimitServer(maxConnections int32, delay int64) net.Listener {
 				writer.WriteHeader(403)
 				return
 			}
-
-			r := request.Header.Get("Range")
-			if r == "" {
-				writer.Header().Set("Content-Length", fmt.Sprintf("%d", BuildSize))
-				writer.WriteHeader(200)
-				(writer.(http.Flusher)).Flush()
-
-				file, err := os.Open(BuildFile)
-				if err != nil {
-					panic(err)
-				}
-				defer file.Close()
-				slowCopy(sl, writer, file, delay)
-			} else {
-				// split range
-				s := strings.Split(r, "=")
-				if len(s) != 2 {
-					writer.WriteHeader(400)
-					return
-				}
-				s = strings.Split(s[1], "-")
-				if len(s) != 2 {
-					writer.WriteHeader(400)
-					return
-				}
-				start, err := strconv.ParseInt(s[0], 10, 64)
-				if err != nil {
-					writer.WriteHeader(400)
-					return
-				}
-				end, err := strconv.ParseInt(s[1], 10, 64)
-				if err != nil {
-					writer.WriteHeader(400)
-					return
-				}
-				if start < 0 || end < 0 || start > end {
-					writer.WriteHeader(400)
-					return
-				}
-				if end >= BuildSize {
-					end = BuildSize - 1
-				}
-				writer.Header().Set("Content-Length", fmt.Sprintf("%d", end-start+1))
-				writer.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, BuildSize))
-				writer.Header().Set("Accept-Ranges", "bytes")
-				writer.WriteHeader(206)
-				(writer.(http.Flusher)).Flush()
-
-				file, err := os.Open(BuildFile)
-				if err != nil {
-					writer.WriteHeader(500)
-					return
-				}
-				defer file.Close()
-				file.Seek(start, 0)
-				slowCopyN(sl, writer, file, end-start+1, delay)
-			}
+			rangeFileHandle(
+				writer,
+				request,
+				nil,
+				func(file *os.File, n int64) {
+					slowCopyN(sl, writer, file, n, delay)
+				},
+			)
 		})
 		return mux
 	})
 }
 
+// StartTestRangeBugServer simulate bug server:
+// Don't follow Range request rules, always return more data than range, e.g. Range: bytes=0-100, return 150 bytes
+func StartTestRangeBugServer() net.Listener {
+	return startTestServer(func(sl *shutdownListener) http.Handler {
+		mux := http.NewServeMux()
+		mux.HandleFunc("/"+BuildName, func(writer http.ResponseWriter, request *http.Request) {
+			rangeFileHandle(
+				writer,
+				request,
+				func(end int64) int64 {
+					var bugEnd = end
+					if end != 0 {
+						bugEnd = end + 50
+						if bugEnd >= BuildSize {
+							bugEnd = end
+						}
+					}
+					return bugEnd
+				},
+				func(file *os.File, n int64) {
+					io.CopyN(writer, file, n)
+				},
+			)
+		})
+		return mux
+	})
+}
+
+func rangeFileHandle(writer http.ResponseWriter, request *http.Request, modifyEnd func(end int64) int64, iocpN func(file *os.File, n int64)) {
+	r := request.Header.Get("Range")
+	// split range
+	s := strings.Split(r, "=")
+	if len(s) != 2 {
+		writer.WriteHeader(400)
+		return
+	}
+	s = strings.Split(s[1], "-")
+	if len(s) != 2 {
+		writer.WriteHeader(400)
+		return
+	}
+	start, err := strconv.ParseInt(s[0], 10, 64)
+	if err != nil {
+		writer.WriteHeader(400)
+		return
+	}
+	end, err := strconv.ParseInt(s[1], 10, 64)
+	if err != nil {
+		writer.WriteHeader(400)
+		return
+	}
+	if start < 0 || end < 0 || start > end {
+		writer.WriteHeader(400)
+		return
+	}
+	if end >= BuildSize {
+		end = BuildSize - 1
+	}
+
+	if modifyEnd != nil {
+		end = modifyEnd(end)
+	}
+
+	writer.Header().Set("Content-Length", fmt.Sprintf("%d", end-start+1))
+	writer.Header().Set("Content-Range", fmt.Sprintf("bytes %d-%d/%d", start, end, BuildSize))
+	writer.Header().Set("Accept-Ranges", "bytes")
+	writer.WriteHeader(206)
+	(writer.(http.Flusher)).Flush()
+
+	file, err := os.Open(BuildFile)
+	if err != nil {
+		writer.WriteHeader(500)
+		return
+	}
+	defer file.Close()
+	file.Seek(start, 0)
+	iocpN(file, end-start+1)
+}
+
 // slowCopyN copies n bytes from src to dst, speed limit is bytes per second
 func slowCopy(sl *shutdownListener, dst io.Writer, src io.Reader, delay int64) (written int64, err error) {
 	buf := make([]byte, 32*1024)
diff --git a/pkg/download/downloader.go b/pkg/download/downloader.go
index 844396b8..c8c00e63 100644
--- a/pkg/download/downloader.go
+++ b/pkg/download/downloader.go
@@ -208,7 +208,7 @@ func (d *Downloader) Setup() error {
 						if task.Status == base.DownloadStatusRunning {
 							downloadDataChanged = current != task.Progress.Downloaded
 							task.Progress.Used = task.timer.Used()
-							task.Progress.Speed = task.calcSpeed(task.speedArr, current-task.Progress.Downloaded, tick)
+							task.Progress.Speed = task.updateSpeed(current-task.Progress.Downloaded, tick)
 							task.Progress.Downloaded = current
 						}
 
@@ -217,7 +217,7 @@ func (d *Downloader) Setup() error {
 							uploader := task.fetcher.(fetcher.Uploader)
 							currentUploaded := uploader.UploadedBytes()
 							uploadDataChanged = currentUploaded != task.Progress.Uploaded
-							task.Progress.UploadSpeed = task.calcSpeed(task.uploadSpeedArr, currentUploaded-task.Progress.Uploaded, tick)
+							task.Progress.UploadSpeed = task.updateUploadSpeed(currentUploaded-task.Progress.Uploaded, tick)
 							task.Progress.Uploaded = currentUploaded
 						}
 						d.emit(EventKeyProgress, task)
diff --git a/pkg/download/model.go b/pkg/download/model.go
index 085a20f0..3da050ca 100644
--- a/pkg/download/model.go
+++ b/pkg/download/model.go
@@ -100,16 +100,27 @@ func (t *Task) clone() *Task {
 	return util.DeepClone(t)
 }
 
-func (t *Task) calcSpeed(speedArr []int64, downloaded int64, usedTime float64) int64 {
-	speedArr = append(speedArr, downloaded)
-	if len(speedArr) > 6 {
-		speedArr = speedArr[1:]
+func (t *Task) updateSpeed(downloaded int64, usedTime float64) int64 {
+	return calcSpeed(&t.speedArr, downloaded, usedTime)
+}
+
+func (t *Task) updateUploadSpeed(downloaded int64, usedTime float64) int64 {
+	return calcSpeed(&t.uploadSpeedArr, downloaded, usedTime)
+}
+
+func calcSpeed(speedArr *[]int64, downloaded int64, usedTime float64) int64 {
+	*speedArr = append(*speedArr, downloaded)
+	// Record last 5 seconds of download speed to calculate the average speed
+	if len(*speedArr) > int(5.0/usedTime) {
+		*speedArr = (*speedArr)[1:]
 	}
+
 	var total int64
-	for _, v := range speedArr {
+	for _, v := range *speedArr {
 		total += v
 	}
-	return int64(float64(total) / float64(len(speedArr)) / usedTime)
+
+	return int64(float64(total) / float64(len(*speedArr)) / usedTime)
 }
 
 type TaskFilter struct {