diff --git a/digest.go b/digest.go
index 89caa31..d2ee0e6 100644
--- a/digest.go
+++ b/digest.go
@@ -44,11 +44,13 @@
 package digest
 
 import (
+	"bytes"
 	"crypto/md5"
 	"crypto/rand"
 	"errors"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"net/http"
 	"strings"
 )
@@ -240,6 +242,15 @@ func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
 		req2.Header[k] = s
 	}
 
+	// Copy body - we need it twice.
+	if req.Body != nil {
+		body, err := ioutil.ReadAll(req.Body)
+		if err != nil {
+			return nil, err
+		}
+		req.Body = ioutil.NopCloser(bytes.NewBuffer(body))
+		req2.Body = ioutil.NopCloser(bytes.NewBuffer(body))
+	}
 	// Make a request to get the 401 that contains the challenge.
 	resp, err := t.Transport.RoundTrip(req)
 	if err != nil || resp.StatusCode != 401 {