diff --git a/chrome/content/zotero/runJS.html b/chrome/content/zotero/runJS.html
index f79199f74f..5b2a9bce52 100644
--- a/chrome/content/zotero/runJS.html
+++ b/chrome/content/zotero/runJS.html
@@ -17,7 +17,7 @@
 						Run as async function
 					</label>
 				</div>
-				<textarea id="code"></textarea>
+				<textarea id="code" oninput="handleInput()"></textarea>
 			</div>
 			
 			<div class="textbox-container">
diff --git a/chrome/content/zotero/runJS.js b/chrome/content/zotero/runJS.js
index 780656c2f0..888f7035b1 100644
--- a/chrome/content/zotero/runJS.js
+++ b/chrome/content/zotero/runJS.js
@@ -32,6 +32,20 @@ async function run() {
 	resultTextbox.value = Zotero.Utilities.varDump(result);
 }
 
+function handleInput() {
+	var checkbox = document.getElementById('run-as-async');
+	var isAsync = checkbox.checked;
+	if (isAsync) {
+		return;
+	}
+	var code = document.getElementById('code').value;
+	// If `await` is used, switch to async mode
+	if (/^\s*await\s/m.test(code)) {
+		checkbox.checked = true;
+		update();
+	}
+}
+
 window.addEventListener('keypress', function (event) {
 	if (Zotero.isMac) {
 		if (!event.metaKey) {