diff --git a/README.md b/README.md
index 25490e54e..5354b4407 100644
--- a/README.md
+++ b/README.md
@@ -1381,11 +1381,13 @@ const isEven = num => num % 2 === 0;
 
 Checks if the provided integer is a prime number.
 
-Returns `false` if the provided number has positive divisors other than 1 and itself or if the number itself is less than 2.
+Check numbers from `2` to the square root of the given number. 
+Return `false` if any of them divides the given number, else return `true`, unless the number is less than `2`.
 
 ```js
 const isPrime = num => {
-  for (var i = 2; i * i <= num; i++) if (num % i == 0) return false;
+  const boundary = Math.floor(Math.sqrt(num));
+  for (var i = 2; i * i <= boundary; i++) if (num % i == 0) return false;
   return num >= 2;
 };
 // isPrime(11) -> true
diff --git a/docs/index.html b/docs/index.html
index 2751272fd..58e9617c8 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -866,9 +866,11 @@ Returns <code>true</code> if the number is even, <code>false</code> if the numbe
 </code></pre>
 </div></div><br/><div class="card fluid"><div class="section double-padded"><h3 id="isprime">isPrime</h3></div><div class="section double-padded">
 <p>Checks if the provided integer is a prime number.</p>
-<p>Returns <code>false</code> if the provided number has positive divisors other than 1 and itself or if the number itself is less than 2.</p>
+<p>Check numbers from <code>2</code> to the square root of the given number.
+Return <code>false</code> if any of them divides the given number, else return <code>true</code>, unless the number is less than <code>2</code>.</p>
 <pre><code class="language-js">const isPrime = num =&gt; {
-  for (var i = 2; i * i &lt;= num; i++) if (num % i == 0) return false;
+  const boundary = Math.floor(Math.sqrt(num));
+  for (var i = 2; i * i &lt;= boundary; i++) if (num % i == 0) return false;
   return num &gt;= 2;
 };
 // isPrime(11) -&gt; true