diff --git i/tag/lib.php w/tag/lib.php
index a28f1bd..1352439 100644
--- i/tag/lib.php
+++ w/tag/lib.php
@@ -838,7 +838,7 @@ function tag_compute_correlations($mincorrelation = 2) {
          LEFT JOIN {tag_correlation} co 
                 ON co.tagid = ta.tagid 
              WHERE tb.tagid IS NOT NULL 
-          GROUP BY ta.tagid, tb.tagid 
+          GROUP BY ta.tagid, tb.tagid, co.id, co.correlatedtags
             HAVING COUNT(*) > :mincorrelation 
           ORDER BY ta.tagid ASC, COUNT(*) DESC, tb.tagid ASC';
     $rs = $DB->get_recordset_sql($sql, array('mincorrelation' => $mincorrelation));