diff --git a/lisp/url/url-http.el b/lisp/url/url-http.el
index 5832e92..f775e72 100644
--- a/lisp/url/url-http.el
+++ b/lisp/url/url-http.el
@@ -211,15 +211,33 @@ url-http-find-free-connection
     (if connection
 	(url-http-mark-connection-as-busy host port connection))))
 
+(defun url-http--user-agent-default-string ()
+  "Compute a default User-Agent string based on `url-privacy-level'."
+  (let ((package-info (when url-package-name
+                        (format "%s/%s" url-package-name url-package-version)))
+        (emacs-info (unless (and (listp url-privacy-level)
+                                 (memq 'emacs url-privacy-level))
+                      (format "GNUEmacs/%s" emacs-version)))
+        (os-info (unless (and (listp url-privacy-level)
+                              (memq 'os url-privacy-level))
+                   (format "(%s; %s)" url-system-type url-os-type)))
+        (url-info (format "URL/%s" url-version)))
+    (string-join (delq nil (list package-info url-info
+                                 emacs-info os-info))
+                 " ")))
+
 ;; Building an HTTP request
 (defun url-http-user-agent-string ()
   (if (or (eq url-privacy-level 'paranoid)
 	  (and (listp url-privacy-level)
 	       (memq 'agent url-privacy-level)))
       ""
-    (if (functionp url-user-agent)
-        (funcall url-user-agent)
-      url-user-agent)))
+    (format "User-Agent: %s\r\n"
+            (string-trim
+             (cond
+              ((functionp url-user-agent) (funcall url-user-agent))
+              ((stringp url-user-agent) url-user-agent)
+              (t (url-http--user-agent-default-string)))))))
 
 (defun url-http-create-request (&optional ref-url)
   "Create an HTTP request for `url-http-target-url', referred to by REF-URL."
diff --git a/lisp/url/url-vars.el b/lisp/url/url-vars.el
index 960a04a..48a4cbe 100644
--- a/lisp/url/url-vars.el
+++ b/lisp/url/url-vars.el
@@ -116,6 +116,7 @@ url-privacy-level
 Valid symbols are:
 email    -- the email address
 os       -- the operating system info
+emacs    -- the version of Emacs
 lastloc  -- the last location
 agent    -- do not send the User-Agent string
 cookies  -- never accept HTTP cookies
@@ -143,6 +144,7 @@ url-privacy-level
 		(checklist :tag "Custom"
 			   (const :tag "Email address" :value email)
 			   (const :tag "Operating system" :value os)
+			   (const :tag "Emacs version" :value emacs)
 			   (const :tag "Last location" :value lastloc)
 			   (const :tag "Browser identification" :value agent)
 			   (const :tag "No cookies" :value cookie)))
@@ -357,13 +359,11 @@ url-gateway-method
 		(const :tag "Direct connection" :value native))
   :group 'url-hairy)
 
-(defcustom url-user-agent (format "User-Agent: %sURL/%s\r\n"
-				  (if url-package-name
-				      (concat url-package-name "/"
-					      url-package-version " ")
-				    "") url-version)
-  "User Agent used by the URL package for HTTP/HTTPS requests
-Should be a string or a function of no arguments returning a string."
+(defcustom url-user-agent nil
+  "User Agent used by the URL package for HTTP/HTTPS requests.
+Should be a string not including the \"User-Agent:\", or a
+function of no arguments returning a such string.
+If nil, the value is calculated based on `url-privacy-level'."
   :type '(choice (string :tag "A static User-Agent string")
                  (function :tag "Call a function to get the User-Agent string"))
   :version "25.1"