diff --git a/library/HTMLPurifier/DefinitionCacheFactory.php b/library/HTMLPurifier/DefinitionCacheFactory.php
index fd1cc9be..3a0f4616 100644
--- a/library/HTMLPurifier/DefinitionCacheFactory.php
+++ b/library/HTMLPurifier/DefinitionCacheFactory.php
@@ -71,7 +71,7 @@ class HTMLPurifier_DefinitionCacheFactory
             return $this->caches[$method][$type];
         }
         if (isset($this->implementations[$method]) &&
-            class_exists($class = $this->implementations[$method], false)) {
+            class_exists($class = $this->implementations[$method])) {
             $cache = new $class($type);
         } else {
             if ($method != 'Serializer') {
diff --git a/library/HTMLPurifier/LanguageFactory.php b/library/HTMLPurifier/LanguageFactory.php
index 4e35272d..16a4f693 100644
--- a/library/HTMLPurifier/LanguageFactory.php
+++ b/library/HTMLPurifier/LanguageFactory.php
@@ -109,7 +109,7 @@ class HTMLPurifier_LanguageFactory
         } else {
             $class = 'HTMLPurifier_Language_' . $pcode;
             $file  = $this->dir . '/Language/classes/' . $code . '.php';
-            if (file_exists($file) || class_exists($class, false)) {
+            if (file_exists($file) || class_exists($class)) {
                 $lang = new $class($config, $context);
             } else {
                 // Go fallback
diff --git a/library/HTMLPurifier/Lexer.php b/library/HTMLPurifier/Lexer.php
index c21f3649..1f552a17 100644
--- a/library/HTMLPurifier/Lexer.php
+++ b/library/HTMLPurifier/Lexer.php
@@ -101,7 +101,7 @@ class HTMLPurifier_Lexer
                         break;
                     }
 
-                    if (class_exists('DOMDocument', false) &&
+                    if (class_exists('DOMDocument') &&
                         method_exists('DOMDocument', 'loadHTML') &&
                         !extension_loaded('domxml')
                     ) {