diff --git a/buf_reader.go b/buf_reader.go
new file mode 100644
index 00000000..bdafdc8b
--- /dev/null
+++ b/buf_reader.go
@@ -0,0 +1,102 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+)
+
+type bufReader struct {
+	r   io.Reader
+	buf *bytes.Buffer
+	cur int
+}
+
+func newBufReader(r io.Reader, buf *bytes.Buffer) *bufReader {
+	br := bufReader{
+		r:   r,
+		buf: buf,
+	}
+	return &br
+}
+
+func (br *bufReader) Read(p []byte) (int, error) {
+	if err := br.fill(br.cur + len(p)); err != nil {
+		return 0, err
+	}
+
+	n := copy(p, br.buf.Bytes()[br.cur:])
+	br.cur += n
+	return n, nil
+}
+
+func (br *bufReader) ReadByte() (byte, error) {
+	if err := br.fill(br.cur + 1); err != nil {
+		return 0, err
+	}
+
+	b := br.buf.Bytes()[br.cur]
+	br.cur++
+	return b, nil
+}
+
+func (br *bufReader) Discard(n int) (int, error) {
+	if n < 0 {
+		return 0, bufio.ErrNegativeCount
+	}
+	if n == 0 {
+		return 0, nil
+	}
+
+	if err := br.fill(br.cur + n); err != nil {
+		return 0, err
+	}
+
+	n = minInt(n, br.buf.Len()-br.cur)
+	br.cur += n
+	return n, nil
+}
+
+func (br *bufReader) Peek(n int) ([]byte, error) {
+	if n < 0 {
+		return []byte{}, bufio.ErrNegativeCount
+	}
+	if n == 0 {
+		return []byte{}, nil
+	}
+
+	if err := br.fill(br.cur + n); err != nil {
+		return []byte{}, err
+	}
+
+	if n > br.buf.Len()-br.cur {
+		return br.buf.Bytes()[br.cur:], io.EOF
+	}
+
+	return br.buf.Bytes()[br.cur : br.cur+n], nil
+}
+
+func (br *bufReader) Flush() error {
+	_, err := br.buf.ReadFrom(br.r)
+	return err
+}
+
+func (br *bufReader) fill(need int) error {
+	n := need - br.buf.Len()
+	if n <= 0 {
+		return nil
+	}
+
+	n = maxInt(4096, n)
+
+	if _, err := br.buf.ReadFrom(io.LimitReader(br.r, int64(n))); err != nil {
+		return err
+	}
+
+	// Nothing was read, it's EOF
+	if br.cur == br.buf.Len() {
+		return io.EOF
+	}
+
+	return nil
+}
diff --git a/download.go b/download.go
index 2cc46f39..9d856f8e 100644
--- a/download.go
+++ b/download.go
@@ -142,13 +142,15 @@ func readAndCheckImage(r io.Reader, contentLength int) (*imageData, error) {
 		r = &limitReader{r: r, left: conf.MaxSrcFileSize}
 	}
 
-	imgtype, err := checkTypeAndDimensions(io.TeeReader(r, buf))
+	br := newBufReader(r, buf)
+
+	imgtype, err := checkTypeAndDimensions(br)
 	if err != nil {
 		cancel()
 		return nil, err
 	}
 
-	if _, err = buf.ReadFrom(r); err != nil {
+	if err = br.Flush(); err != nil {
 		cancel()
 		return nil, newError(404, err.Error(), msgSourceImageIsUnreachable).SetUnexpected(conf.ReportDownloadingErrors)
 	}