diff --git a/csrf.php b/csrf.php
index 902ff64..bb34ea6 100644
--- a/csrf.php
+++ b/csrf.php
@@ -98,12 +98,14 @@ class csrf
       return TRUE;
     // Migrate from unique format to multiple CSRF tokens format
     // The new format is : array (token => the last used time)
-    if (isset ($_SESSION["domframework"]["csrf"]["csrfStart"]))
+    if (isset ($_SESSION["domframework"]["csrf"]["csrf"]) &&
+        isset ($_SESSION["domframework"]["csrf"]["csrfStart"]))
     {
       $_SESSION["domframework"]["csrf"] = array (
         $_SESSION["domframework"]["csrf"]["csrf"] =>
          $_SESSION["domframework"]["csrf"]["csrfStart"]
       );
+      unset ($_SESSION["domframework"]["csrf"]["csrfStart"]);
     }
     if (! isset ($_SESSION["domframework"]["csrf"]))
     {