diff --git a/common/httpx/httpx.go b/common/httpx/httpx.go
index 039f4c4c..594c7003 100644
--- a/common/httpx/httpx.go
+++ b/common/httpx/httpx.go
@@ -8,7 +8,6 @@ import (
 	"net"
 	"net/http"
 	"net/url"
-	"os"
 	"strconv"
 	"strings"
 	"time"
@@ -153,9 +152,8 @@ func New(options *Options) (*HTTPX, error) {
 		DisableKeepAlives: true,
 	}
 
-	if httpx.Options.Protocol == "http11" {
+	if isHTTP11Protocol(httpx.Options.Protocol) {
 		// disable http2
-		_ = os.Setenv("GODEBUG", "http2client=0")
 		transport.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{}
 	}
 
@@ -182,6 +180,10 @@ func New(options *Options) (*HTTPX, error) {
 		Timeout:       httpx.Options.Timeout,
 		CheckRedirect: redirectFunc,
 	}, retryablehttpOptions)
+	if isHTTP11Protocol(httpx.Options.Protocol) {
+		// Keep retryablehttp-go on HTTP/1.1 as well when it retries internally.
+		httpx.client.HTTPClient2 = httpx.client.HTTPClient
+	}
 
 	transport2 := &http2.Transport{
 		TLSClientConfig: &tls.Config{
@@ -212,6 +214,10 @@ func New(options *Options) (*HTTPX, error) {
 	return httpx, nil
 }
 
+func isHTTP11Protocol(protocol Proto) bool {
+	return strings.EqualFold(string(protocol), string(HTTP11))
+}
+
 // Do http request
 func (h *HTTPX) Do(req *retryablehttp.Request, unsafeOptions UnsafeOptions) (*Response, error) {
 	timeStart := time.Now()
diff --git a/common/httpx/httpx_test.go b/common/httpx/httpx_test.go
index 7da6ad12..82e5e28a 100644
--- a/common/httpx/httpx_test.go
+++ b/common/httpx/httpx_test.go
@@ -28,3 +28,29 @@ func TestDo(t *testing.T) {
 		require.Greater(t, len(resp.Raw), 800)
 	})
 }
+
+func TestHTTP11DisablesRetryableHTTP2Fallback(t *testing.T) {
+	opts := DefaultOptions
+	opts.Protocol = HTTP11
+
+	ht, err := New(&opts)
+	require.NoError(t, err)
+	require.Same(t, ht.client.HTTPClient, ht.client.HTTPClient2)
+}
+
+func TestHTTP11MixedCaseDisablesRetryableHTTP2Fallback(t *testing.T) {
+	opts := DefaultOptions
+	opts.Protocol = Proto("HTTP11")
+
+	ht, err := New(&opts)
+	require.NoError(t, err)
+	require.Same(t, ht.client.HTTPClient, ht.client.HTTPClient2)
+}
+
+func TestDefaultProtocolKeepsRetryableHTTP2Fallback(t *testing.T) {
+	opts := DefaultOptions
+
+	ht, err := New(&opts)
+	require.NoError(t, err)
+	require.NotSame(t, ht.client.HTTPClient, ht.client.HTTPClient2)
+}