diff --git a/phpBB/includes/acp/acp_main.php b/phpBB/includes/acp/acp_main.php
index a279f2b489..e122273284 100644
--- a/phpBB/includes/acp/acp_main.php
+++ b/phpBB/includes/acp/acp_main.php
@@ -185,30 +185,29 @@ class acp_main
 
 						// Resync post counts
 						$start = 0;
+						$step = ($config['num_posts']) ? (max((int) ($config['num_posts'] / 5), 20000)) : 20000;
+
+						$db->sql_query('UPDATE ' . USERS_TABLE . ' SET user_posts = 0');
 
 						do
 						{
-							$sql = 'SELECT COUNT(p.post_id) AS num_posts, u.user_id
-								FROM ' . USERS_TABLE . ' u
-								LEFT JOIN  ' . POSTS_TABLE . ' p ON (u.user_id = p.poster_id AND p.post_postcount = 1 AND p.post_approved = 1)
-								GROUP BY u.user_id
-								ORDER BY u.user_id ASC';
-							$result = $db->sql_query_limit($sql, 200, $start);
+							$sql = 'SELECT COUNT(post_id) AS num_posts, poster_id
+								FROM ' . POSTS_TABLE . '
+								WHERE post_id BETWEEN ' . ($start + 1) . ' AND ' . ($start + $step) . '
+									AND post_postcount = 1 AND post_approved = 1
+								GROUP BY poster_id';
+							$result = $db->sql_query($sql);
 
 							if ($row = $db->sql_fetchrow($result))
 							{
-								$i = 0;
-
 								do
 								{
-									$sql = 'UPDATE ' . USERS_TABLE . " SET user_posts = {$row['num_posts']} WHERE user_id = {$row['user_id']}";
+									$sql = 'UPDATE ' . USERS_TABLE . " SET user_posts = user_posts + {$row['num_posts']} WHERE user_id = {$row['poster_id']}";
 									$db->sql_query($sql);
-
-									$i++;
 								}
 								while ($row = $db->sql_fetchrow($result));
 
-								$start = ($i < 200) ? 0 : $start + 200;
+								$start += $step;
 							}
 							else
 							{