diff --git a/content_scripts/dictionary-plus.js b/content_scripts/dictionary-plus.js
index da33fb0..4cabd55 100644
--- a/content_scripts/dictionary-plus.js
+++ b/content_scripts/dictionary-plus.js
@@ -543,7 +543,10 @@ function saveWord(key) {
 
 
 function updatePopUp(key, data) {
-  const popupNode = OPENED_POPUPS[key].node;
+  const popupNode = OPENED_POPUPS[key]?.node;
+
+  // If user clicks out before definition is retrieved, `OPEN_POPUPS[key]` will not exist
+  if (popupNode === undefined) return;
 
   const popup = popupNode.shadowRoot;
 
@@ -667,4 +670,4 @@ function onStorageChange(changes, area) {
   SETTINGS = settings.newValue;
 }
 
-browser.storage.onChanged.addListener(onStorageChange);
\ No newline at end of file
+browser.storage.onChanged.addListener(onStorageChange);