diff --git a/http2/transport.go b/http2/transport.go
index ccb885ff0..576203953 100644
--- a/http2/transport.go
+++ b/http2/transport.go
@@ -651,9 +651,6 @@ func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
 	}
 	hasTrailers := trailers != ""
 
-	body, contentLen := bodyAndLength(req)
-	hasBody := body != nil
-
 	cc.mu.Lock()
 	cc.lastActive = time.Now()
 	if cc.closed || !cc.canTakeNewRequestLocked() {
@@ -661,6 +658,9 @@ func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
 		return nil, errClientConnUnusable
 	}
 
+	body, contentLen := bodyAndLength(req)
+	hasBody := body != nil
+
 	// TODO(bradfitz): this is a copy of the logic in net/http. Unify somewhere?
 	var requestedGzip bool
 	if !cc.t.disableCompression() &&
diff --git a/http2/transport_test.go b/http2/transport_test.go
index 1bc5c4b4b..bfc54000c 100644
--- a/http2/transport_test.go
+++ b/http2/transport_test.go
@@ -2468,3 +2468,24 @@ func TestTransportBodyDoubleEndStream(t *testing.T) {
 		defer res.Body.Close()
 	}
 }
+
+// golang.org/issue/17071 -- don't sniff the first byte of the request body
+// before we've determined that the ClientConn is usable.
+func TestRoundTripDoesntConsumeRequestBodyEarly(t *testing.T) {
+	const body = "foo"
+	req, _ := http.NewRequest("POST", "http://foo.com/", ioutil.NopCloser(strings.NewReader(body)))
+	cc := &ClientConn{
+		closed: true,
+	}
+	_, err := cc.RoundTrip(req)
+	if err != errClientConnUnusable {
+		t.Fatalf("RoundTrip = %v; want errClientConnUnusable", err)
+	}
+	slurp, err := ioutil.ReadAll(req.Body)
+	if err != nil {
+		t.Errorf("ReadAll = %v", err)
+	}
+	if string(slurp) != body {
+		t.Errorf("Body = %q; want %q", slurp, body)
+	}
+}