diff --git a/demos/html/tinymce6/src/app.js b/demos/html/tinymce6/src/app.js
index f5e3c679b..a2d8e8574 100644
--- a/demos/html/tinymce6/src/app.js
+++ b/demos/html/tinymce6/src/app.js
@@ -20,7 +20,51 @@ tinymce.init({
   },
 
   // This option allows us to introduce mathml formulas
-  extended_valid_elements: '*[.*]',
+  extended_valid_elements: [
+    'math[*]',
+    'maction[*]',
+    'malignmark[*]',
+    'maligngroup[*]',
+    'menclose[*]',
+    'merror[*]',
+    'mfenced[*]',
+    'mfrac[*]',
+    'mglyph[*]',
+    'mi[*]',
+    'mlabeledtr[*]',
+    'mlongdiv[*]',
+    'mmultiscripts[*]',
+    'mn[*]',
+    'mo[*]',
+    'mover[*]',
+    'mpadded[*]',
+    'mphantom[*]',
+    'mprescripts[*]',
+    'none[*]',
+    'mroot[*]',
+    'mrow[*]',
+    'ms[*]',
+    'mscarries[*]',
+    'mscarry[*]',
+    'msgroup[*]',
+    'msline[*]',
+    'mspace[*]',
+    'msqrt[*]',
+    'msrow[*]',
+    'mstack[*]',
+    'mstyle[*]',
+    'msub[*]',
+    'msubsup[*]',
+    'msup[*]',
+    'mtable[*]',
+    'mtd[*]',
+    'mtext[*]',
+    'mtr[*]',
+    'munder[*]',
+    'munderover[*]',
+    'semantics[*]',
+    'annotation[*]',
+  ].join(),
   // We recommend to set 'draggable_modal' to true to avoid overlapping issues
   // with the different UI modal dialog windows implementations between core and third-party plugins on TinyMCE.
   // @see: https://github.com/wiris/html-integrations/issues/134#issuecomment-905448642
diff --git a/packages/tinymce6/editor_plugin.src.js b/packages/tinymce6/editor_plugin.src.js
index 87050a297..6617711ff 100644
--- a/packages/tinymce6/editor_plugin.src.js
+++ b/packages/tinymce6/editor_plugin.src.js
@@ -185,54 +185,6 @@ export const currentInstance = null;
 
   tinymce.PluginManager.add(pluginName, (editor, url) => ({ // eslint-disable-line no-unused-vars
     init(editor) {
-      // Array with MathML valid alements.
-      const validMathML = [
-        'math[*]',
-        'maction[*]',
-        'malignmark[*]',
-        'maligngroup[*]',
-        'menclose[*]',
-        'merror[*]',
-        'mfenced[*]',
-        'mfrac[*]',
-        'mglyph[*]',
-        'mi[*]',
-        'mlabeledtr[*]',
-        'mlongdiv[*]',
-        'mmultiscripts[*]',
-        'mn[*]',
-        'mo[*]',
-        'mover[*]',
-        'mpadded[*]',
-        'mphantom[*]',
-        'mprescripts[*]',
-        'none[*]',
-        'mroot[*]',
-        'mrow[*]',
-        'ms[*]',
-        'mscarries[*]',
-        'mscarry[*]',
-        'msgroup[*]',
-        'msline[*]',
-        'mspace[*]',
-        'msqrt[*]',
-        'msrow[*]',
-        'mstack[*]',
-        'mstyle[*]',
-        'msub[*]',
-        'msubsup[*]',
-        'msup[*]',
-        'mtable[*]',
-        'mtd[*]',
-        'mtext[*]',
-        'mtr[*]',
-        'munder[*]',
-        'munderover[*]',
-        'semantics[*]',
-        'annotation[*]',
-      ];
-
-      editor.options.set('extended_valid_elements', validMathML.join());
       // editor.schema.addCustomElements(validMathML.join());
 
       // editor.settings.extended_valid_elements += ; // eslint-disable-line no-param-reassign