diff --git a/form.php b/form.php
index dc6ddfc..d7704f8 100644
--- a/form.php
+++ b/form.php
@@ -314,6 +314,8 @@ class form
   public function convertDate ($inputDate, $inputFormat, $outputFormat)
   {
     $date = DateTime::CreateFromFormat ($inputFormat, $inputDate);
+    if ($date === false)
+      return $inputDate;
     $errors = $date->getLastErrors();
     if ($errors["warning_count"] > 0 || $errors["error_count"] > 0)
       return $inputDate;