Index: src/wp-includes/formatting.php
===================================================================
--- src/wp-includes/formatting.php	(revision 32850)
+++ src/wp-includes/formatting.php	(working copy)
@@ -688,6 +688,12 @@
 		$quote_style = ENT_NOQUOTES;
 	}
 
+	if ( ! $double_encode ) {
+		// Guarantee every &entity; is valid, convert &garbage; into &garbage;
+		// This is required for PHP < 5.4.0 because ENT_HTML401 flag is unavailable.
+		$string = wp_kses_normalize_entities( $string );
+	}
+
 	$string = @htmlspecialchars( $string, $quote_style, $charset, $double_encode );
 
 	// Backwards compatibility
Index: tests/phpunit/tests/formatting/EscHtml.php
===================================================================
--- tests/phpunit/tests/formatting/EscHtml.php	(revision 32850)
+++ tests/phpunit/tests/formatting/EscHtml.php	(working copy)
@@ -34,7 +34,7 @@
 
 	function test_ignores_existing_entities() {
 		$source = '&#038; &#x00A3; &#x22; &amp;';
-		$res = '&#038; &#x00A3; &#x22; &amp;';
+		$res = '&#038; &#xA3; &#x22; &amp;';
 		$this->assertEquals( $res, esc_html($source) );
 	}
 }
Index: tests/phpunit/tests/formatting/WPSpecialchars.php
===================================================================
--- tests/phpunit/tests/formatting/WPSpecialchars.php	(revision 32850)
+++ tests/phpunit/tests/formatting/WPSpecialchars.php	(working copy)
@@ -85,7 +85,7 @@
 		return array(
 			array(
 				'This & that, this &amp; that, &#8212; &quot; &QUOT; &Uacute; &nbsp; &#34; &#034; &#0034; &#x00022; &#x22; &dollar; &times;',
-				'This &amp; that, this &amp; that, &#8212; &quot; &amp;QUOT; &Uacute; &nbsp; &#34; &#034; &#0034; &#x00022; &#x22; &amp;dollar; &times;',
+				'This &amp; that, this &amp; that, &#8212; &quot; &amp;QUOT; &Uacute; &nbsp; &#034; &#034; &#034; &#x22; &#x22; &amp;dollar; &times;',
 			),
 			array(
 				'&& &&amp; &amp;&amp; &amp;;',