Index: src/wp-includes/js/tinymce/plugins/wpview/plugin.js
===================================================================
--- src/wp-includes/js/tinymce/plugins/wpview/plugin.js	(revision 30992)
+++ src/wp-includes/js/tinymce/plugins/wpview/plugin.js	(working copy)
@@ -158,21 +158,41 @@
 	}
 
 	function adjustToolbarPosition( viewNode ) {
-		var delta = 0,
+		var viewNodeRect, iframeRect, toolbarWidth, bodyWidth, pageX,
+			delta = 0,
+			buffer = 5, // Used for keeping the toolbar a little bit (5px) on the inside of the editor.
+			toolbarTopOffset = 43,
+			body = editor.getBody(),
+			prop = 'left',
 			toolbar = editor.$( viewNode ).find( '.toolbar' ),
 			editorToolbar = tinymce.$( editor.editorContainer ).find( '.mce-toolbar-grp' )[0],
 			editorToolbarBottom = ( editorToolbar && editorToolbar.getBoundingClientRect().bottom ) || 0;
-		
-		if ( toolbar.length && editor.iframeElement ) {
-			// 48 = 43 for the toolbar + 5 buffer
-			delta = viewNode.getBoundingClientRect().top + editor.iframeElement.getBoundingClientRect().top - editorToolbarBottom - 48;
+
+		if ( ! toolbar.length || ! editor.iframeElement ) {
+			return;
 		}
 
+		viewNodeRect = viewNode.getBoundingClientRect();
+		iframeRect = editor.iframeElement.getBoundingClientRect();
+		bodyWidth = body.clientWidth;
+		toolbarWidth = toolbar[0].clientWidth;
+		delta = viewNodeRect.top + iframeRect.top - editorToolbarBottom - toolbarTopOffset - buffer;
+		pageX = editor.getWin().pageXOffset || editor.getDoc().documentElement.scrollLeft || 0;
+
+		if ( editor.$( body ).hasClass( 'rtl' ) ) {
+			prop = 'right';
+			pageX = pageX && pageX * -1;
+		}
+
 		if ( delta < 0 ) {
-			toolbar.removeClass( 'mce-arrow-down' ).css({ top: ( -43 + delta * -1 ) });
+			toolbar.removeClass( 'mce-arrow-down' ).css({ top: ( -toolbarTopOffset + delta * -1 ) });
 		} else if ( delta > 0 && ! toolbar.hasClass( 'mce-arrow-down' ) ) {
 			toolbar.addClass( 'mce-arrow-down' ).css({ top: '' });
 		}
+
+		if ( viewNode.clientWidth > bodyWidth ) {
+			toolbar.css( prop, ( bodyWidth - toolbarWidth ) / 2 + pageX );
+		}
 	}
 
 	/**
Index: src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
===================================================================
--- src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(revision 30992)
+++ src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(working copy)
@@ -340,6 +340,12 @@
 	margin-bottom: 8px;
 }
 
+.rtl .wpview-wrap .toolbar {
+	left: auto;
+	right: 45%;
+	right: calc(50% - 32px);
+}
+
 .wpview-wrap[data-mce-selected] .toolbar {
 	display: block;
 }