diff --git a/challenges/02-javascript-algorithms-and-data-structures/es6.json b/challenges/02-javascript-algorithms-and-data-structures/es6.json
index f09ca0fe03..11a52afc96 100644
--- a/challenges/02-javascript-algorithms-and-data-structures/es6.json
+++ b/challenges/02-javascript-algorithms-and-data-structures/es6.json
@@ -37,6 +37,8 @@
         "<blockquote>let camper = 'James';<br>let camper = 'David'; // throws an error</blockquote>",        
         "This error can be seen in the console of your browser.",
         "So unlike <code>var</code>, when using <code>let</code>, a variable with the same name can only be declared once.", 
+        "Note the <code>\"use strict\"</code>. This enables Strict Mode, which catches common coding mistakes and \"unsafe\" actions. For instance:",
+        "<blockquote>\"use strict\";<br>x = 3.14; // throws an error because x is not declared</blockquote>",
         "<hr>",
         "Update the code so it only uses the <code>let</code> keyword.",
         "<strong>Note</strong><br>Remember that since <code>let</code> prevents variables from being overridden, you will need to remove one of the declarations entirely."