Index: src/wp-includes/formatting.php
===================================================================
--- src/wp-includes/formatting.php	(revision 25951)
+++ src/wp-includes/formatting.php	(working copy)
@@ -1601,8 +1601,15 @@
 function make_clickable( $text ) {
 	$r = '';
 	$textarr = preg_split( '/(<[^<>]+>)/', $text, -1, PREG_SPLIT_DELIM_CAPTURE ); // split out HTML tags
+	$nested_code_pre = 0; // Keep track of how many levels link is nested inside <pre> or <code>
 	foreach ( $textarr as $piece ) {
-		if ( empty( $piece ) || ( $piece[0] == '<' && ! preg_match('|^<\s*[\w]{1,20}+://|', $piece) ) ) {
+
+		if ( preg_match( '|^<code[\s>]|', $piece ) || preg_match( '|^<pre[\s>]|', $piece ) )
+			$nested_code_pre++;
+		elseif ( ( '</code>' === $piece || '</pre>' === $piece ) && $nested_code_pre )
+			$nested_code_pre--;
+
+		if ( $nested_code_pre || empty( $piece ) || ( $piece[0] === '<' && ! preg_match( '|^<\s*[\w]{1,20}+://|', $piece ) ) ) {
 			$r .= $piece;
 			continue;
 		}
Index: tests/phpunit/tests/formatting/MakeClickable.php
===================================================================
--- tests/phpunit/tests/formatting/MakeClickable.php	(revision 25951)
+++ tests/phpunit/tests/formatting/MakeClickable.php	(working copy)
@@ -289,6 +289,47 @@
 	}
 
 	/**
+	 * ticket 23756
+	 */
+	function test_no_links_inside_pre_or_code() {
+		$before = array(
+			'<pre>http://wordpress.org</pre>',
+			'<code>http://wordpress.org</code>',
+			'<pre class="foobar" id="foo">http://wordpress.org</pre>',
+			'<code class="foobar" id="foo">http://wordpress.org</code>',
+			'<precustomtag>http://wordpress.org</precustomtag>',
+			'<codecustomtag>http://wordpress.org</codecustomtag>',
+			'URL before pre http://wordpress.org<pre>http://wordpress.org</pre>',
+			'URL before code http://wordpress.org<code>http://wordpress.org</code>',
+			'URL after pre <pre>http://wordpress.org</pre>http://wordpress.org',
+			'URL after code <code>http://wordpress.org</code>http://wordpress.org',
+			'URL before and after pre http://wordpress.org<pre>http://wordpress.org</pre>http://wordpress.org',
+			'URL before and after code http://wordpress.org<code>http://wordpress.org</code>http://wordpress.org',
+			'code inside pre <pre>http://wordpress.org <code>http://wordpress.org</code> http://wordpress.org</pre>',
+		);
+
+		$expected = array(
+			'<pre>http://wordpress.org</pre>',
+			'<code>http://wordpress.org</code>',
+			'<pre class="foobar" id="foo">http://wordpress.org</pre>',
+			'<code class="foobar" id="foo">http://wordpress.org</code>',
+			'<precustomtag><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a></precustomtag>',
+			'<codecustomtag><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a></codecustomtag>',
+			'URL before pre <a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a><pre>http://wordpress.org</pre>',
+			'URL before code <a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a><code>http://wordpress.org</code>',
+			'URL after pre <pre>http://wordpress.org</pre><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a>',
+			'URL after code <code>http://wordpress.org</code><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a>',
+			'URL before and after pre <a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a><pre>http://wordpress.org</pre><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a>',
+			'URL before and after code <a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a><code>http://wordpress.org</code><a href="http://wordpress.org" rel="nofollow">http://wordpress.org</a>',
+			'code inside pre <pre>http://wordpress.org <code>http://wordpress.org</code> http://wordpress.org</pre>',
+		);
+
+		foreach ($before as $key => $url) {
+			$this->assertEquals($expected[$key], make_clickable($url));
+		}
+	}
+
+	/**
 	 * @ticket 16892
 	 */
 	function test_click_inside_html() {