Index: src/wp-includes/class-wp-editor.php
===================================================================
--- src/wp-includes/class-wp-editor.php	(revision 51066)
+++ src/wp-includes/class-wp-editor.php	(working copy)
@@ -1663,14 +1663,9 @@
 		?>
 
 		( function() {
-			var init, id, $wrap;
+			var initialize = function() {
+				var init, id, $wrap;
 
-			if ( typeof tinymce !== 'undefined' ) {
-				if ( tinymce.Env.ie && tinymce.Env.ie < 11 ) {
-					tinymce.$( '.wp-editor-wrap ' ).removeClass( 'tmce-active' ).addClass( 'html-active' );
-					return;
-				}
-
 				for ( id in tinyMCEPreInit.mceInit ) {
 					init = tinyMCEPreInit.mceInit[id];
 					$wrap = tinymce.$( '#wp-' + id + '-wrap' );
@@ -1685,6 +1680,18 @@
 				}
 			}
 
+			if ( typeof tinymce !== 'undefined' ) {
+				if ( tinymce.Env.ie && tinymce.Env.ie < 11 ) {
+					tinymce.$( '.wp-editor-wrap ' ).removeClass( 'tmce-active' ).addClass( 'html-active' );
+				} else {
+					if ( document.readyState === 'complete' || document.readyState === 'interactive' ) {
+						initialize();
+					} else {
+						document.addEventListener( 'DOMContentLoaded', initialize );
+					}
+				}
+			}
+
 			if ( typeof quicktags !== 'undefined' ) {
 				for ( id in tinyMCEPreInit.qtInit ) {
 					quicktags( tinyMCEPreInit.qtInit[id] );