diff --git a/Gruntfile.js b/Gruntfile.js
index a48351ec31..fd048b1cca 100644
--- a/Gruntfile.js
+++ b/Gruntfile.js
@@ -172,14 +172,29 @@ module.exports = function(grunt) {
 				]
 			}
 		},
-		cssjanus: {
-			core: {
-				options: {
+		rtlcss: {
+			options: {
+				// rtlcss options
+				config: {
+					swapLeftRightInUrl: false,
 					swapLtrRtlInUrl: false,
-					processContent: function( src ) {
-						return src.replace( /url\((.+?)\.css\)/g, 'url($1-rtl.css)' );
-					}
+					autoRename: false,
+					preserveDirectives: true,
+					stringMap: [
+						{
+							name: 'import-rtl-stylesheet',
+							search: [ '.css' ],
+							replace: [ '-rtl.css' ],
+							options: {
+								scope: 'url',
+								ignoreCase: false
+							}
+						}
+					]
 				},
+				saveUnmodified: false
+			},
+			core: {
 				expand: true,
 				cwd: SOURCE_DIR,
 				dest: BUILD_DIR,
@@ -190,11 +205,6 @@ module.exports = function(grunt) {
 				]
 			},
 			colors: {
-				options: {
-					processContent: function( src ) {
-						return src.replace( /([^/]+)\.css/gi, '$1-rtl.css' );
-					}
-				},
 				expand: true,
 				cwd: BUILD_DIR,
 				dest: BUILD_DIR,
@@ -503,7 +513,7 @@ module.exports = function(grunt) {
 					SOURCE_DIR + 'wp-admin/css/*.css',
 					SOURCE_DIR + 'wp-includes/css/*.css'
 				],
-				tasks: ['cssjanus:dynamic'],
+				tasks: ['rtlcss:dynamic'],
 				options: {
 					spawn: false,
 					interval: 2000
@@ -522,7 +532,7 @@ module.exports = function(grunt) {
 	// Register tasks.
 
 	// RTL task.
-	grunt.registerTask('rtl', ['cssjanus:core', 'cssjanus:colors']);
+	grunt.registerTask('rtl', ['rtlcss:core', 'rtlcss:colors']);
 
 	// Color schemes task.
 	grunt.registerTask('colors', ['sass:colors', 'autoprefixer:colors']);
@@ -576,7 +586,7 @@ module.exports = function(grunt) {
 	//
 	// On `watch:all`, automatically updates the `copy:dynamic` and `clean:dynamic`
 	// configurations so that only the changed files are updated.
-	// On `watch:rtl`, automatically updates the `cssjanus:dynamic` configuration.
+	// On `watch:rtl`, automatically updates the `rtlcss:dynamic` configuration.
 	grunt.event.on('watch', function( action, filepath, target ) {
 		if ( target !== 'all' && target !== 'rtl' ) {
 			return;
@@ -588,6 +598,6 @@ module.exports = function(grunt) {
 
 		grunt.config(['clean', 'dynamic', 'src'], cleanSrc);
 		grunt.config(['copy', 'dynamic', 'src'], copySrc);
-		grunt.config(['cssjanus', 'dynamic', 'src'], copySrc);
+		grunt.config(['rtlcss', 'dynamic', 'src'], copySrc);
 	});
 };
diff --git a/package.json b/package.json
index 5668db6659..3fd05d84c0 100644
--- a/package.json
+++ b/package.json
@@ -22,10 +22,10 @@
     "grunt-contrib-qunit": "~0.5.2",
     "grunt-contrib-uglify": "~0.6.0",
     "grunt-contrib-watch": "~0.6.1",
-    "grunt-cssjanus": "~0.2.4",
     "grunt-jsvalidate": "~0.2.2",
     "grunt-legacy-util": "^0.2.0",
     "grunt-patch-wordpress": "~0.3.0",
+    "grunt-rtlcss": "~1.5.1",
     "grunt-sass": "~0.16.0",
     "matchdep": "~0.3.0"
   }
diff --git a/src/wp-admin/css/about.css b/src/wp-admin/css/about.css
index 2e3d8ae9f2..8ce72b8ebd 100644
--- a/src/wp-admin/css/about.css
+++ b/src/wp-admin/css/about.css
@@ -263,6 +263,7 @@
 	opacity: 0;
 }
 
+/* rtl:ignore */
 .about-wrap .dfw-container .overlay-image.from-left {
 	-webkit-transform: translate3d(-100%, 0, 0);
 	transform: translate3d(-100%, 0, 0);
@@ -296,7 +297,7 @@
 .about-wrap .feature-list svg {
 	float: left;
 	clear: left;
-	margin: 15px 15px 0 0 ;
+	margin: 15px 15px 0 0;
 	height: 90px;
 	width: 90px;
 	background-color: #cccccc;
diff --git a/src/wp-admin/css/admin-menu.css b/src/wp-admin/css/admin-menu.css
index 729e432945..2076c5c450 100644
--- a/src/wp-admin/css/admin-menu.css
+++ b/src/wp-admin/css/admin-menu.css
@@ -592,6 +592,7 @@ ul#adminmenu > li.current > a.current:after {
 	-moz-osx-font-smoothing: grayscale;
 }
 
+/* rtl:ignore */
 .folded #collapse-button div:after,
 .rtl #collapse-button div:after {
 	-webkit-transform: rotate(180deg);
@@ -723,6 +724,7 @@ li#wp-admin-bar-menu-toggle {
 		background: none;
 	}
 
+	/* rtl:ignore */
 	.auto-fold #collapse-button div:after {
 		-webkit-transform: rotate(180deg);
 		-ms-transform: rotate(180deg);
diff --git a/src/wp-admin/css/common.css b/src/wp-admin/css/common.css
index 300fbfa41c..51b6a7d9cf 100644
--- a/src/wp-admin/css/common.css
+++ b/src/wp-admin/css/common.css
@@ -390,12 +390,12 @@ ol.ol-decimal > li {
 	margin: 0 0 0.5em;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .ltr {
 	direction: ltr;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .code,
 code {
 	font-family: Consolas, Monaco, monospace;
@@ -2375,12 +2375,12 @@ div.action-links {
 	background: #f3f3f3;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .section {
 	direction: ltr;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .section ul,
 #plugin-information .section ol {
 	list-style-type: disc;
@@ -2408,7 +2408,7 @@ div.action-links {
 	box-shadow: 0 1px 2px rgba( 0, 0, 0, 0.3 );
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information #section-screenshots li p {
 	font-style: italic;
 	padding-left: 20px;
@@ -2420,7 +2420,7 @@ div.action-links {
 	border: 1px solid #ccc;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .review {
 	overflow: hidden; /* clearfix */
 	width: 100%;
@@ -2432,7 +2432,7 @@ div.action-links {
 	overflow: hidden; /* clearfix */
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .review-title-section h4 {
 	display: inline-block;
 	float: left;
@@ -2445,24 +2445,24 @@ div.action-links {
 	padding-top: 2px;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .reviewer-info .avatar {
 	float: left;
 	margin: 4px 6px 0 0;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .reviewer-info .star-rating {
 	float: left;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .review-meta {
 	float: left;
 	margin-left: 0.75em;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #plugin-information .review-body {
 	float: left;
 	width: 100%;
@@ -2710,7 +2710,7 @@ img {
 	outline: none;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #template textarea,
 #docs-list {
 	direction: ltr;
diff --git a/src/wp-admin/css/edit.css b/src/wp-admin/css/edit.css
index b1a1428cba..9c89c00886 100644
--- a/src/wp-admin/css/edit.css
+++ b/src/wp-admin/css/edit.css
@@ -1310,7 +1310,6 @@ table.links-table {
 	transition-timing-function: ease-in-out;
 }
 
-/* @noflip */
 .focus-on #adminmenuback,
 .focus-on #adminmenuwrap {
 	-webkit-transform: translateX( -100% );
@@ -1318,14 +1317,6 @@ table.links-table {
 	transform: translateX( -100% );
 }
 
-/* @noflip */
-.rtl.focus-on #adminmenuback,
-.rtl.focus-on #adminmenuwrap {
-	-webkit-transform: translateX( 100% );
-	-ms-transform: translateX( 100% );
-	transform: translateX( 100% );
-}
-
 .focus-off #adminmenuback,
 .focus-off #adminmenuwrap {
 	-webkit-transform: translateX( 0 );
diff --git a/src/wp-admin/css/forms.css b/src/wp-admin/css/forms.css
index 0758a02824..47de611809 100644
--- a/src/wp-admin/css/forms.css
+++ b/src/wp-admin/css/forms.css
@@ -61,7 +61,7 @@ textarea:focus {
 	box-shadow: 0 0 2px rgba( 30, 140, 190, 0.8 );
 }
 
-/* @noflip */
+/* rtl:ignore */
 input[type="email"],
 input[type="url"] {
 	direction: ltr;
diff --git a/src/wp-admin/css/install.css b/src/wp-admin/css/install.css
index 57be437295..dbeb3e630b 100644
--- a/src/wp-admin/css/install.css
+++ b/src/wp-admin/css/install.css
@@ -237,7 +237,7 @@ submit {
 	background-color: #ffebe8;
 }
 
-/* @noflip */
+/* rtl:ignore */
 #dbname,
 #uname,
 #pwd,
diff --git a/src/wp-admin/css/themes.css b/src/wp-admin/css/themes.css
index a1a8bb257f..1b9f276536 100644
--- a/src/wp-admin/css/themes.css
+++ b/src/wp-admin/css/themes.css
@@ -1524,6 +1524,7 @@ body.full-overlay-active {
 	text-decoration: none !important;
 }
 
+/* rtl:ignore */
 .wp-full-overlay.collapsed .collapse-sidebar-arrow:before,
 .rtl .wp-full-overlay .collapse-sidebar-arrow:before {
 	-webkit-transform: rotate(180deg);
diff --git a/src/wp-includes/css/editor.css b/src/wp-includes/css/editor.css
index d05a3fca78..0ebac83752 100644
--- a/src/wp-includes/css/editor.css
+++ b/src/wp-includes/css/editor.css
@@ -2112,12 +2112,12 @@ i.mce-i-hr:before {
 	font-family: Tahoma, sans-serif;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .mce-rtl .mce-flow-layout .mce-flow-layout-item > div {
 	direction: rtl;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .mce-rtl .mce-listbox i.mce-caret {
 	left: 6px;
 }
diff --git a/src/wp-includes/css/jquery-ui-dialog.css b/src/wp-includes/css/jquery-ui-dialog.css
index 9383ad95c2..65de83a1cd 100644
--- a/src/wp-includes/css/jquery-ui-dialog.css
+++ b/src/wp-includes/css/jquery-ui-dialog.css
@@ -128,7 +128,7 @@
 	bottom: -5px;
 	left: 0;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-e {
 	cursor: e-resize;
 	width: 7px;
@@ -136,7 +136,7 @@
 	top: 0;
 	height: 100%;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-w {
 	cursor: w-resize;
 	width: 7px;
@@ -144,7 +144,7 @@
 	top: 0;
 	height: 100%;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-se {
 	cursor: se-resize;
 	width: 12px;
@@ -152,7 +152,7 @@
 	right: 1px;
 	bottom: 1px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-sw {
 	cursor: sw-resize;
 	width: 9px;
@@ -160,7 +160,7 @@
 	left: -5px;
 	bottom: -5px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-nw {
 	cursor: nw-resize;
 	width: 9px;
@@ -168,7 +168,7 @@
 	left: -5px;
 	top: -5px;
 }
-/* @noflip */
+/* rtl:ignore */
 .ui-resizable-ne {
 	cursor: ne-resize;
 	width: 9px;
diff --git a/src/wp-includes/css/media-views.css b/src/wp-includes/css/media-views.css
index d9ea92f775..2157a3c9ef 100644
--- a/src/wp-includes/css/media-views.css
+++ b/src/wp-includes/css/media-views.css
@@ -886,13 +886,11 @@
 	overflow: hidden;
 }
 
-/* @noflip */
 .wp-core-ui .attachment .thumbnail img {
 	top: 0;
 	left: 0;
 }
 
-/* @noflip */
 .wp-core-ui .attachment .thumbnail .centered {
 	position: absolute;
 	top: 0;
diff --git a/src/wp-includes/css/wp-pointer.css b/src/wp-includes/css/wp-pointer.css
index 1d69823f11..5c457b40dc 100644
--- a/src/wp-includes/css/wp-pointer.css
+++ b/src/wp-includes/css/wp-pointer.css
@@ -110,11 +110,11 @@
 	padding-bottom: 13px;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-left {
 	padding-left: 13px;
 }
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-right {
 	margin-left: -13px;
 	padding-right: 13px;
@@ -168,14 +168,14 @@
 	content: ' ';
 }
 
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-left .wp-pointer-arrow {
 	left: 0;
 	border-width: 13px 13px 13px 0;
 	border-right-color: #ccc;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-left .wp-pointer-arrow-inner {
 	left: 1px;
 	margin-left: -13px;
@@ -186,14 +186,14 @@
 	content: ' ';
 }
 
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-right .wp-pointer-arrow {
 	right: 0;
 	border-width: 13px 0 13px 13px;
 	border-left-color: #ccc;
 }
 
-/* @noflip */
+/* rtl:ignore */
 .wp-pointer-right .wp-pointer-arrow-inner {
 	right: 1px;
 	margin-right: -13px;