diff --git a/mod/assign/upgradelib.php b/mod/assign/upgradelib.php
index 89f15a27ee3..4ddb9e778a2 100644
--- a/mod/assign/upgradelib.php
+++ b/mod/assign/upgradelib.php
@@ -257,7 +257,7 @@ class assign_upgrade_manager {
 
         } catch (Exception $exception) {
             $rollback = true;
-            $log .= get_string('conversionexception', 'mod_assign', $exception->error);
+            $log .= get_string('conversionexception', 'mod_assign', $exception->getMessage());
         }
 
         if ($rollback) {