diff --git a/client_test.go b/client_test.go
index 987135011b..579a1236c5 100644
--- a/client_test.go
+++ b/client_test.go
@@ -21,8 +21,8 @@ import (
 
 func TestClientURLAuth(t *testing.T) {
 	cases := map[string]string{
-		"user:pass@": "dXNlcjpwYXNz",
-		"foo:@":      "Zm9vOg==",
+		"user:pass@": "Basic dXNlcjpwYXNz",
+		"foo:@":      "Basic Zm9vOg==",
 		":@":         "",
 		"@":          "",
 		"":           "",
diff --git a/http.go b/http.go
index 99782a852c..d10c9b161d 100644
--- a/http.go
+++ b/http.go
@@ -1155,7 +1155,8 @@ func (req *Request) Write(w *bufio.Writer) error {
 			// So we are free to use RequestHeader.bufKV.value as a scratch pad for
 			// the base64 encoding.
 			nl := len(uri.username) + len(uri.password) + 1
-			tl := nl + base64.StdEncoding.EncodedLen(nl)
+			nb := nl + len(strBasicSpace)
+			tl := nb + base64.StdEncoding.EncodedLen(nl)
 			if tl > cap(req.Header.bufKV.value) {
 				req.Header.bufKV.value = make([]byte, 0, tl)
 			}
@@ -1163,9 +1164,9 @@ func (req *Request) Write(w *bufio.Writer) error {
 			buf = append(buf, uri.username...)
 			buf = append(buf, strColon...)
 			buf = append(buf, uri.password...)
-			buf = buf[:tl]
-			base64.StdEncoding.Encode(buf[nl:], buf[:nl])
-			req.Header.SetBytesKV(strAuthorization, buf[nl:])
+			buf = append(buf, strBasicSpace...)
+			base64.StdEncoding.Encode(buf[nb:tl], buf[:nl])
+			req.Header.SetBytesKV(strAuthorization, buf[nl:tl])
 		}
 	}
 
diff --git a/strings.go b/strings.go
index 343544ad18..12f1926308 100644
--- a/strings.go
+++ b/strings.go
@@ -81,4 +81,5 @@ var (
 	strBytes               = []byte("bytes")
 	strTextSlash           = []byte("text/")
 	strApplicationSlash    = []byte("application/")
+	strBasicSpace          = []byte("Basic ")
 )