diff --git a/CRM/Dedupe/Merger.php b/CRM/Dedupe/Merger.php
index 400d3364c6a6..2aff9fea1bd5 100644
--- a/CRM/Dedupe/Merger.php
+++ b/CRM/Dedupe/Merger.php
@@ -1914,7 +1914,7 @@ public static function getMergeCacheKeyString($rule_group_id, $group_id, $criter
     $cacheKeyString = "merge {$contactType}";
     $cacheKeyString .= $rule_group_id ? "_{$rule_group_id}" : '_0';
     $cacheKeyString .= $group_id ? "_{$group_id}" : '_0';
-    $cacheKeyString .= !empty($criteria) ? serialize($criteria) : '_0';
+    $cacheKeyString .= !empty($criteria) ? md5(serialize($criteria)) : '_0';
     if ($checkPermissions) {
       $contactID = CRM_Core_Session::getLoggedInContactID();
       if (!$contactID) {