diff --git a/core/editor.js b/core/editor.js
index 0546ffe5eb..515add0f4b 100644
--- a/core/editor.js
+++ b/core/editor.js
@@ -9,6 +9,9 @@ import equal from 'deep-equal';
 import extend from 'extend';
 
 
+const ASCII = /^[ -~]*$/;
+
+
 class Editor {
   constructor(scroll) {
     this.scroll = scroll;
@@ -189,6 +192,7 @@ class Editor {
     let oldDelta = this.delta;
     if (mutations.length === 1 &&
         mutations[0].type === 'characterData' &&
+        mutations[0].target.data.match(ASCII) &&
         Parchment.find(mutations[0].target)) {
       // Optimization for character changes
       let textBlot = Parchment.find(mutations[0].target);