diff --git a/xhprof_html/callgraph.php b/xhprof_html/callgraph.php
index a56b8781..46fc6a52 100644
--- a/xhprof_html/callgraph.php
+++ b/xhprof_html/callgraph.php
@@ -33,7 +33,7 @@
 // are at the same level.
 $GLOBALS['XHPROF_LIB_ROOT'] = dirname(__FILE__) . '/../xhprof_lib';
 
-include_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
+require_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
 
 ini_set('max_execution_time', 100);
 
diff --git a/xhprof_html/index.php b/xhprof_html/index.php
index 36293360..f21d32fd 100644
--- a/xhprof_html/index.php
+++ b/xhprof_html/index.php
@@ -35,7 +35,7 @@
 // are at the same level.
 $GLOBALS['XHPROF_LIB_ROOT'] = dirname(__FILE__) . '/../xhprof_lib';
 
-include_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
+require_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
 
 // param name, its type, and default value
 $params = array('run'        => array(XHPROF_STRING_PARAM, ''),
diff --git a/xhprof_html/typeahead.php b/xhprof_html/typeahead.php
index 2ae2e383..ba98e0c3 100644
--- a/xhprof_html/typeahead.php
+++ b/xhprof_html/typeahead.php
@@ -25,8 +25,8 @@
 // are at the same level.
 $GLOBALS['XHPROF_LIB_ROOT'] = dirname(__FILE__) . '/../xhprof_lib';
 
-include_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
+require_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/xhprof.php';
 
 $xhprof_runs_impl = new XHProfRuns_Default();
 
-include_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/typeahead_common.php';
+require_once $GLOBALS['XHPROF_LIB_ROOT'].'/display/typeahead_common.php';