diff --git a/http3/roundtrip.go b/http3/roundtrip.go
index ff813536..95506cac 100644
--- a/http3/roundtrip.go
+++ b/http3/roundtrip.go
@@ -110,6 +110,10 @@ func (r *RoundTripper) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.
 		closeRequestBody(req)
 		return nil, errors.New("http3: nil Request.URL")
 	}
+	if req.URL.Scheme != "https" {
+		closeRequestBody(req)
+		return nil, fmt.Errorf("http3: unsupported protocol scheme: %s", req.URL.Scheme)
+	}
 	if req.URL.Host == "" {
 		closeRequestBody(req)
 		return nil, errors.New("http3: no Host in request URL")
@@ -118,10 +122,6 @@ func (r *RoundTripper) RoundTripOpt(req *http.Request, opt RoundTripOpt) (*http.
 		closeRequestBody(req)
 		return nil, errors.New("http3: nil Request.Header")
 	}
-	if req.URL.Scheme != "https" {
-		closeRequestBody(req)
-		return nil, fmt.Errorf("http3: unsupported protocol scheme: %s", req.URL.Scheme)
-	}
 	for k, vv := range req.Header {
 		if !httpguts.ValidHeaderFieldName(k) {
 			return nil, fmt.Errorf("http3: invalid http header field name %q", k)