diff --git a/core/custom_field_api.php b/core/custom_field_api.php
index 0aecf70243..1cc7e04143 100644
--- a/core/custom_field_api.php
+++ b/core/custom_field_api.php
@@ -1182,7 +1182,7 @@ function custom_field_validate( $p_field_id, $p_value ) {
 		case CUSTOM_FIELD_TYPE_DATE:
 			// gpc_get_cf for date returns the value from strftime
 			// either false (php >= 5.1)  or -1 (php < 5.1) for failure
-			$t_valid &= ( $p_value !== false ) && ( $p_value > 0 );
+			$t_valid &= ( $p_value == null ) || ( ( $p_value !== false ) && ( $p_value > 0 ) );
 			break;
 		case CUSTOM_FIELD_TYPE_ENUM:
 		case CUSTOM_FIELD_TYPE_EMAIL: