diff --git a/http2/transport.go b/http2/transport.go
index 0acb7bc..21a5f52 100644
--- a/http2/transport.go
+++ b/http2/transport.go
@@ -2485,6 +2485,7 @@
 
 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