diff --git a/packages/ckeditor5-math/src/mathediting.ts b/packages/ckeditor5-math/src/mathediting.ts
index bd026829c..166b209e4 100644
--- a/packages/ckeditor5-math/src/mathediting.ts
+++ b/packages/ckeditor5-math/src/mathediting.ts
@@ -59,7 +59,7 @@ export default class MathEditing extends Plugin {
 			allowWhere: '$text',
 			isInline: true,
 			isObject: true,
-			allowAttributes: [ 'equation', 'type', 'display' ]
+			allowAttributes: [ 'equation', 'type', 'display', 'fontSize' ]
 		} );
 
 		schema.register( 'mathtex-display', {