diff --git a/http2/transport.go b/http2/transport.go
index 76a92e0ca6..2482f7bf92 100644
--- a/http2/transport.go
+++ b/http2/transport.go
@@ -2525,6 +2525,7 @@ func strSliceContains(ss []string, s string) bool {
 
 type erringRoundTripper struct{ err error }
 
+func (rt erringRoundTripper) RoundTripErr() error                             { return rt.err }
 func (rt erringRoundTripper) RoundTrip(*http.Request) (*http.Response, error) { return nil, rt.err }
 
 // gzipReader wraps a response body so it can lazily