diff --git a/db.php b/db.php
index 6b4d62c..2c0b69e 100644
--- a/db.php
+++ b/db.php
@@ -657,6 +657,25 @@ function initDatabase(): void {
             $db->query("DELETE FROM sites");
         }
     } catch (\Throwable $e) { /* ohitetaan */ }
+
+    // Migraatio: aseta vanhojen kansioiden customer_id dokumenttien perusteella
+    try {
+        $orphans = $db->query("SELECT id FROM document_folders WHERE customer_id IS NULL");
+        while ($row = $orphans->fetch_assoc()) {
+            $fid = $row['id'];
+            // Hae yleisin customer_id kansion dokumenteista
+            $res = $db->query("SELECT customer_id, COUNT(*) AS cnt FROM documents WHERE folder_id = '$fid' AND customer_id IS NOT NULL GROUP BY customer_id ORDER BY cnt DESC LIMIT 1");
+            $top = $res->fetch_assoc();
+            if ($top && $top['customer_id']) {
+                $cid = $db->real_escape_string($top['customer_id']);
+                $db->query("UPDATE document_folders SET customer_id = '$cid' WHERE id = '$fid'");
+            } else {
+                // Kansio ei sisällä dokumentteja asiakkaalla → poistetaan
+                $db->query("UPDATE documents SET folder_id = NULL WHERE folder_id = '$fid'");
+                $db->query("DELETE FROM document_folders WHERE id = '$fid'");
+            }
+        }
+    } catch (\Throwable $e) { /* ohitetaan */ }
 }
 
 // ==================== YRITYKSET ====================