date/date_elements.inc |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/date/date_elements.inc b/date/date_elements.inc
index 4cc07f2..bcb6931 100644
--- a/date/date_elements.inc
+++ b/date/date_elements.inc
@@ -521,6 +521,9 @@ function date_combo_validate($element, &$form_state) {
       }
 
       if (empty($errors)) {
+        if ($to_date_empty) {
+          $item[$to_field] = null;
+        }
         form_set_value($element, $item, $form_state);
       }
     }