diff --git a/src/URI.js b/src/URI.js
index 6f7fd572..f63ad6c6 100644
--- a/src/URI.js
+++ b/src/URI.js
@@ -240,10 +240,16 @@
     ws: '80',
     wss: '443'
   };
+  // list of protocols which always require a hostname
+  URI.hostProtocols = [
+    'http',
+    'https'
+  ];
+
   // allowed hostname characters according to RFC 3986
   // ALPHA DIGIT "-" "." "_" "~" "!" "$" "&" "'" "(" ")" "*" "+" "," ";" "=" %encoded
   // I've never seen a (non-IDN) hostname other than: ALPHA DIGIT . -
-  URI.invalid_hostname_characters = /[^a-zA-Z0-9\.-]/;
+  URI.invalid_hostname_characters = /[^a-zA-Z0-9\.\-:]/;
   // map DOM Elements to their URI attribute
   URI.domAttributes = {
     'a': 'href',
@@ -575,6 +581,12 @@
       string = '/' + string;
     }
 
+    URI.ensureValidHostname(parts.hostname, parts.protocol);
+
+    if (parts.port) {
+      URI.ensureValidPort(parts.port);
+    }
+
     return string.substring(pos) || '/';
   };
   URI.parseAuthority = function(string, parts) {
@@ -1015,22 +1027,44 @@
     return string;
   };
 
-  URI.ensureValidHostname = function(v) {
+  URI.ensureValidHostname = function(v, protocol) {
     // Theoretically URIs allow percent-encoding in Hostnames (according to RFC 3986)
     // they are not part of DNS and therefore ignored by URI.js
 
-    if (v.match(URI.invalid_hostname_characters)) {
+    var hasHostname = !!v; // not null and not an empty string
+    var hasProtocol = !!protocol;
+    var rejectEmptyHostname = false;
+
+    if (hasProtocol) {
+      rejectEmptyHostname = arrayContains(URI.hostProtocols, protocol);
+    }
+
+    if (rejectEmptyHostname && !hasHostname) {
+      throw new TypeError('Hostname cannot be empty, if protocol is ' + protocol);
+    } else if (v && v.match(URI.invalid_hostname_characters)) {
       // test punycode
       if (!punycode) {
         throw new TypeError('Hostname "' + v + '" contains characters other than [A-Z0-9.-] and Punycode.js is not available');
       }
-
       if (punycode.toASCII(v).match(URI.invalid_hostname_characters)) {
-        throw new TypeError('Hostname "' + v + '" contains characters other than [A-Z0-9.-]');
+        throw new TypeError('Hostname "' + v + '" contains characters other than [A-Z0-9.:-]');
       }
     }
   };
 
+  URI.ensureValidPort = function (v) {
+    if (!v) {
+      return;
+    }
+
+    var port = Number(v);
+    if (Number.isInteger(port) && (port > 0) && (port < 65536)) {
+      return;
+    }
+
+    throw new TypeError('Port "' + v + '" is not a valid port');
+  };
+
   // noConflict
   URI.noConflict = function(removeAll) {
     if (removeAll) {
@@ -1288,9 +1322,7 @@
           v = v.substring(1);
         }
 
-        if (v.match(/[^0-9]/)) {
-          throw new TypeError('Port "' + v + '" contains characters other than [0-9]');
-        }
+        URI.ensureValidPort(v);
       }
     }
     return _port.call(this, v, build);
@@ -1308,6 +1340,7 @@
       }
 
       v = x.hostname;
+      URI.ensureValidHostname(v, this._parts.protocol);
     }
     return _hostname.call(this, v, build);
   };
@@ -1426,8 +1459,12 @@
         v += '.';
       }
 
+      if (v.indexOf(':') !== -1) {
+        throw new TypeError('Domains cannot contain colons');
+      }
+
       if (v) {
-        URI.ensureValidHostname(v);
+        URI.ensureValidHostname(v, this._parts.protocol);
       }
 
       this._parts.hostname = this._parts.hostname.replace(replace, v);
@@ -1466,7 +1503,11 @@
         throw new TypeError('cannot set domain empty');
       }
 
-      URI.ensureValidHostname(v);
+      if (v.indexOf(':') !== -1) {
+        throw new TypeError('Domains cannot contain colons');
+      }
+
+      URI.ensureValidHostname(v, this._parts.protocol);
 
       if (!this._parts.hostname || this.is('IP')) {
         this._parts.hostname = v;
diff --git a/test/test.js b/test/test.js
index 1cc2ce5d..8ebf8623 100644
--- a/test/test.js
+++ b/test/test.js
@@ -124,6 +124,26 @@
     ok(u instanceof URI, 'instanceof URI');
     ok(u._parts.hostname !== undefined, 'host undefined');
   });
+  test('function URI(string) with invalid port "port" throws', function () {
+    raises(function () {
+      new URI('http://example.org:port');
+    }, TypeError, "throws TypeError");
+  });
+  test('function URI(string) with invalid port "0" throws', function () {
+    raises(function () {
+      new URI('http://example.org:0');
+    }, TypeError, "throws TypeError");
+  });
+  test('function URI(string) with invalid port "65536" throws', function () {
+    raises(function () {
+      new URI('http://example.org:65536');
+    }, TypeError, "throws TypeError");
+  });
+  test('function URI(string) with protocol and without hostname should throw', function () {
+    raises(function () {
+      new URI('http://');
+    }, TypeError, "throws TypeError");
+  });
   test('new URI(string, string)', function() {
     // see http://dvcs.w3.org/hg/url/raw-file/tip/Overview.html#constructor
     var u = new URI('../foobar.html', 'http://example.org/hello/world.html');
@@ -223,13 +243,16 @@
     equal(u.hostname(), 'abc.foobar.lala', 'hostname changed');
     equal(u+'', 'http://abc.foobar.lala/foo.html', 'hostname changed url');
 
-    u.hostname('');
-    equal(u.hostname(), '', 'hostname removed');
-    equal(u+'', 'http:///foo.html', 'hostname removed url');
-
     raises(function() {
       u.hostname('foo\\bar.com');
     }, TypeError, 'Failing backslash detection in hostname');
+
+    raises(function() {
+      u.hostname('');
+    }, TypeError, "Trying to set an empty hostname with http(s) protocol throws a TypeError");
+    raises(function() {
+      u.hostname(null);
+    }, TypeError, "Trying to set hostname to null with http(s) protocol throws a TypeError");
   });
   test('port', function() {
     var u = new URI('http://example.org/foo.html');
@@ -1338,11 +1361,6 @@
         url: 'file:///C:/skyclan/snipkit',
         base: 'http://example.com/foo/bar',
         result: 'file:///C:/skyclan/snipkit'
-      }, {
-        name: 'absolute passthru - generic empty-hostname - urljoin (#328)',
-        url: 'http:///foo',
-        base: 'http://example.com/foo/bar',
-        result: 'http:///foo'
       }, {
         name: 'file paths - urljoin',
         url: 'anotherFile',