diff --git a/client.go b/client.go
index 753f5f19..11450a9b 100644
--- a/client.go
+++ b/client.go
@@ -423,26 +423,9 @@ func (c *Client) WriteStream(path string, stream io.Reader, _ os.FileMode) (err
 		return err
 	}
 
-	contentLength := int64(0)
-	if seeker, ok := stream.(io.Seeker); ok {
-		contentLength, err = seeker.Seek(0, io.SeekEnd)
-		if err != nil {
-			return err
-		}
-
-		_, err = seeker.Seek(0, io.SeekStart)
-		if err != nil {
-			return err
-		}
-	} else {
-		buffer := bytes.NewBuffer(make([]byte, 0, 1024*1024 /* 1MB */))
-
-		contentLength, err = io.Copy(buffer, stream)
-		if err != nil {
-			return err
-		}
-
-		stream = buffer
+	contentLength, err := getContentLength(stream)
+	if err != nil {
+		return err
 	}
 
 	s, err := c.put(path, stream, contentLength)
diff --git a/utils.go b/utils.go
index d466160e..dee2a1f9 100644
--- a/utils.go
+++ b/utils.go
@@ -111,3 +111,30 @@ func (l *limitedReadCloser) Read(buf []byte) (int, error) {
 func (l *limitedReadCloser) Close() error {
 	return l.rc.Close()
 }
+
+func getContentLength(reader io.Reader) (int64, error) {
+	contentLength := int64(-1)
+	switch reader := reader.(type) {
+	case *bytes.Buffer:
+		contentLength = int64(reader.Len())
+	case io.Seeker:
+		currentPos, err := reader.Seek(0, io.SeekCurrent)
+		if err != nil {
+			return -1, err
+		}
+
+		endPos, err := reader.Seek(0, io.SeekEnd)
+		if err != nil {
+			return -1, err
+		}
+
+		contentLength = endPos - currentPos
+
+		_, err = reader.Seek(currentPos, io.SeekStart)
+		if err != nil {
+			return -1, err
+		}
+	}
+
+	return contentLength, nil
+}