diff --git a/phpBB/common.php b/phpBB/common.php
index 524c05ae70..061290dcea 100644
--- a/phpBB/common.php
+++ b/phpBB/common.php
@@ -59,15 +59,6 @@ if (!defined('PHPBB_INSTALLED'))
 	exit;
 }
 
-if (defined('DEBUG_EXTRA'))
-{
-	$base_memory_usage = 0;
-	if (function_exists('memory_get_usage'))
-	{
-		$base_memory_usage = memory_get_usage();
-	}
-}
-
 // Load Extensions
 // dl() is deprecated and disabled by default as of PHP 5.3.
 if (!empty($load_extensions) && function_exists('dl'))
diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 8f41e18db6..688c7f2000 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -4627,15 +4627,13 @@ function page_footer($run_cron = true)
 
 		if ($auth->acl_get('a_') && defined('DEBUG_EXTRA'))
 		{
-			if (function_exists('memory_get_usage'))
+			if (function_exists('memory_get_peak_usage'))
 			{
-				if ($memory_usage = memory_get_usage())
+				if ($memory_usage = memory_get_peak_usage())
 				{
-					global $base_memory_usage;
-					$memory_usage -= $base_memory_usage;
 					$memory_usage = get_formatted_filesize($memory_usage);
 
-					$debug_output .= ' | Memory Usage: ' . $memory_usage;
+					$debug_output .= ' | Peak Memory Usage: ' . $memory_usage;
 				}
 			}
 
diff --git a/phpBB/includes/functions_acp.php b/phpBB/includes/functions_acp.php
index c3806dc786..36e22e069f 100644
--- a/phpBB/includes/functions_acp.php
+++ b/phpBB/includes/functions_acp.php
@@ -106,15 +106,13 @@ function adm_page_footer($copyright_html = true)
 
 		if ($auth->acl_get('a_') && defined('DEBUG_EXTRA'))
 		{
-			if (function_exists('memory_get_usage'))
+			if (function_exists('memory_get_peak_usage'))
 			{
-				if ($memory_usage = memory_get_usage())
+				if ($memory_usage = memory_get_peak_usage())
 				{
-					global $base_memory_usage;
-					$memory_usage -= $base_memory_usage;
 					$memory_usage = get_formatted_filesize($memory_usage);
 
-					$debug_output .= ' | Memory Usage: ' . $memory_usage;
+					$debug_output .= ' | Peak Memory Usage: ' . $memory_usage;
 				}
 			}