diff --git a/test/lib/test_period.ml b/test/lib/test_period.ml
index 4814366..b8fa7bd 100644
--- a/test/lib/test_period.ml
+++ b/test/lib/test_period.ml
@@ -27,8 +27,8 @@ let test_to_8601 =
     make_test "one million" ~input:1_000_000. ~expected:"1970-01-12T13:46:40Z";
     make_test "one billion" ~input:1_000_000_000.
       ~expected:"2001-09-09T01:46:40Z";
-    make_test "one trillion" ~input:1_000_000_000_000.
-      ~expected:"33658-09-27T01:46:40Z";
+    make_test "ten billions" ~input:10_000_000_000.
+      ~expected:"2286-11-20T17:46:40Z";
   ]
 
 let test_with_period = []