diff --git a/tests/ISO8601_PRINTER.ml b/tests/ISO8601_PRINTER.ml
index 125d1de..b3c4643 100644
--- a/tests/ISO8601_PRINTER.ml
+++ b/tests/ISO8601_PRINTER.ml
@@ -22,6 +22,7 @@ let suite =
   OUnit.(>:::) "[PRINTER]" [
     OUnit.(>:::) "[PRINTER DATE]"
           [
+            date (-413596800.) "1956-11-23";
             date 0. "1970-01-01" ;
             date (24. *. 3600.) "1970-01-02" ;
             date (31. *. 24. *. 3600.) "1970-02-01" ;