diff --git a/lib/url.js b/lib/url.js
index c5be960cbe..b8ba3fb1dd 100644
--- a/lib/url.js
+++ b/lib/url.js
@@ -390,6 +390,11 @@ Url.prototype.format = function() {
   if (hash && hash.charAt(0) !== '#') hash = '#' + hash;
   if (search && search.charAt(0) !== '?') search = '?' + search;
 
+  pathname = pathname.replace(/[?#]/g, function(match) {
+    return encodeURIComponent(match);
+  });
+  search = search.replace('#', '%23');
+
   return protocol + host + pathname + search + hash;
 };
 
diff --git a/test/simple/test-url.js b/test/simple/test-url.js
index 8a4cb40faf..6630da1025 100644
--- a/test/simple/test-url.js
+++ b/test/simple/test-url.js
@@ -943,6 +943,50 @@ var formatTests = {
     'protocol': 'coap',
     'host': '[fedc:ba98:7654:3210:fedc:ba98:7654:3210]:61616',
     'pathname': '/s/stopButton'
+  },
+
+  // encode context-specific delimiters in path and query, but do not touch
+  // other non-delimiter chars like `%`.
+  // <https://github.com/joyent/node/issues/4082>
+
+  // `#`,`?` in path
+  '/path/to/%%23%3F+=&.txt?foo=theA1#bar' : {
+    href : '/path/to/%%23%3F+=&.txt?foo=theA1#bar',
+    pathname: '/path/to/%#?+=&.txt',
+    query: {
+      foo: 'theA1'
+    },
+    hash: "#bar"
+  },
+
+  // `#`,`?` in path + `#` in query
+  '/path/to/%%23%3F+=&.txt?foo=the%231#bar' : {
+    href : '/path/to/%%23%3F+=&.txt?foo=the%231#bar',
+    pathname: '/path/to/%#?+=&.txt',
+    query: {
+      foo: 'the#1'
+    },
+    hash: "#bar"
+  },
+
+  // `?` and `#` in path and search
+  'http://ex.com/foo%3F100%m%23r?abc=the%231?&foo=bar#frag': {
+    href: 'http://ex.com/foo%3F100%m%23r?abc=the%231?&foo=bar#frag',
+    protocol: 'http:',
+    hostname: 'ex.com',
+    hash: '#frag',
+    search: '?abc=the#1?&foo=bar',
+    pathname: '/foo?100%m#r',
+  },
+
+  // `?` and `#` in search only
+  'http://ex.com/fooA100%mBr?abc=the%231?&foo=bar#frag': {
+    href: 'http://ex.com/fooA100%mBr?abc=the%231?&foo=bar#frag',
+    protocol: 'http:',
+    hostname: 'ex.com',
+    hash: '#frag',
+    search: '?abc=the#1?&foo=bar',
+    pathname: '/fooA100%mBr',
   }
 };
 for (var u in formatTests) {