diff --git a/api/get_user_messages.php b/api/get_user_messages.php
index b3412f5..3dae4e8 100644
--- a/api/get_user_messages.php
+++ b/api/get_user_messages.php
@@ -66,11 +66,13 @@ try {
 
     $params = ['user_id' => $userId];
     if ($before) {
-        $sql .= " AND (c.created_at < :before";
-        $params['before'] = $before;
+        $sql .= " AND (c.created_at < :before_lt";
+        $params['before_lt'] = $before;
         if ($beforeId) {
             // Incluir mensajes con mismo timestamp pero id menor (paginación estable)
-            $sql .= " OR (c.created_at = :before AND c.id < :before_id)";
+            // Usamos placeholder distinto para evitar duplicar el mismo nombre en la query
+            $sql .= " OR (c.created_at = :before_eq AND c.id < :before_id)";
+            $params['before_eq'] = $before;
             $params['before_id'] = $beforeId;
         }
         $sql .= ")";