diff --git a/markdown-processor/src/main/java/com/yydcdut/markdown/live/CodeBlockLive.java b/markdown-processor/src/main/java/com/yydcdut/markdown/live/CodeBlockLive.java
index 0830f83..29060d2 100644
--- a/markdown-processor/src/main/java/com/yydcdut/markdown/live/CodeBlockLive.java
+++ b/markdown-processor/src/main/java/com/yydcdut/markdown/live/CodeBlockLive.java
@@ -66,14 +66,14 @@ public void onTextChanged(CharSequence s, int start, int before, int after) {
         if (after == 0) {
             return;
         }
-        String addString = s.subSequence(start, (start + after) > s.length() ? s.length() : (start + after)).toString();
+        String addString = s.subSequence(Utils.safePosition(start, s), Utils.safePosition(start + after, s)).toString();
         String beforeString = null;
         String afterString = null;
         if (start + 1 <= s.length()) {
-            afterString = s.subSequence(start, start + 1).toString();
+            afterString = s.subSequence(Utils.safePosition(start, s), Utils.safePosition(start + 1, s)).toString();
         }
         if (start > 0) {
-            beforeString = s.subSequence(start - 1, start).toString();
+            beforeString = s.subSequence(Utils.safePosition(start - 1, s), Utils.safePosition(start, s)).toString();
         }
         //``` --> `1``(``1`)(```1)(1```)
         if (SyntaxUtils.isNeedFormat(SyntaxKey.KEY_CODE_BLOCK_SINGLE, addString, beforeString, afterString)) {
@@ -81,6 +81,7 @@ public void onTextChanged(CharSequence s, int start, int before, int after) {
         }
     }
 
+
     private void format(Editable editable, int start) {
         Utils.removeSpans(editable, start, MDCodeBlockSpan.class);
         Syntax syntax = EditFactory.create().getCodeBlockSyntax(mMarkdownConfiguration);
diff --git a/markdown-processor/src/main/java/com/yydcdut/markdown/utils/Utils.java b/markdown-processor/src/main/java/com/yydcdut/markdown/utils/Utils.java
index 828c69c..988868b 100644
--- a/markdown-processor/src/main/java/com/yydcdut/markdown/utils/Utils.java
+++ b/markdown-processor/src/main/java/com/yydcdut/markdown/utils/Utils.java
@@ -321,4 +321,14 @@ public static char getChar(char[] array, int index) {
         return array[index];
     }
 
+    /**
+     * get position safely
+     *
+     * @param position the position
+     * @param s        the CharSequence
+     * @return the safe position
+     */
+    public static int safePosition(int position, CharSequence s) {
+        return position > s.length() ? s.length() : (position < 0 ? 0 : position);
+    }
 }