diff --git a/demo/demo.js b/demo/demo.js
index 8267431..c222835 100644
--- a/demo/demo.js
+++ b/demo/demo.js
@@ -24,7 +24,7 @@ function showOutput(el) {
   try {
     const re = toRegExp(input, flags, {
       allowBestEffort: optionAllowBestEffortValue,
-      maxRecursionDepth: +optionMaxRecursionDepthValue,
+      maxRecursionDepth: optionMaxRecursionDepthValue === '' ? null : +optionMaxRecursionDepthValue,
       optimize: optionOptimizeValue,
       target: optionTargetValue,
     });
diff --git a/demo/index.html b/demo/index.html
index 8683445..3f5cc33 100644
--- a/demo/index.html
+++ b/demo/index.html
@@ -50,7 +50,7 @@ <h2>Try it</h2>
           <code>allowBestEffort</code>
         </label>
         <label>
-          <input type="number" id="option-max-recursion-depth" value="6" min="2" max="100" onchange="setOptionMaxRecursionDepth(this.value)">
+          <input type="number" id="option-max-recursion-depth" value="6" min="2" max="100" onchange="setOptionMaxRecursionDepth(this.value)" onkeyup="setOptionMaxRecursionDepth(this.value)">
           <code>maxRecursionDepth</code>
         </label>
         <label>