diff --git a/h2quic/client.go b/h2quic/client.go
index 91e33791c..c0a711731 100644
--- a/h2quic/client.go
+++ b/h2quic/client.go
@@ -144,8 +144,7 @@ func (c *client) Do(req *http.Request) (*http.Response, error) {
 		return nil, errors.New("quic http2: unsupported scheme")
 	}
 	if authorityAddr("https", hostnameFromRequest(req)) != c.hostname {
-		utils.Debugf("%s vs %s", req.Host, c.hostname)
-		return nil, errors.New("h2quic Client BUG: Do called for the wrong client")
+		return nil, fmt.Errorf("h2quic Client BUG: RoundTrip called for the wrong client (expected %s, got %s)", c.hostname, req.Host)
 	}
 
 	hasBody := (req.Body != nil)
diff --git a/h2quic/client_test.go b/h2quic/client_test.go
index a9451f5aa..890a27079 100644
--- a/h2quic/client_test.go
+++ b/h2quic/client_test.go
@@ -212,7 +212,7 @@ var _ = Describe("Client", func() {
 				req, err := http.NewRequest("https", "https://quic.clemente.io:1336/foobar.html", nil)
 				Expect(err).ToNot(HaveOccurred())
 				_, err = client.Do(req)
-				Expect(err).To(MatchError("h2quic Client BUG: Do called for the wrong client"))
+				Expect(err).To(MatchError("h2quic Client BUG: RoundTrip called for the wrong client (expected quic.clemente.io:1337, got quic.clemente.io:1336)"))
 			})
 
 			It("refuses to do plain HTTP requests", func() {