diff --git a/lib/common/tests/iso8601/pcmk__readable_interval_test.c b/lib/common/tests/iso8601/pcmk__readable_interval_test.c
index 43b55410b0..d354975ce2 100644
--- a/lib/common/tests/iso8601/pcmk__readable_interval_test.c
+++ b/lib/common/tests/iso8601/pcmk__readable_interval_test.c
@@ -1,27 +1,29 @@
 /*
  * Copyright 2021 the Pacemaker project contributors
  *
  * The version control history for this file may have further details.
  *
  * This source code is licensed under the GNU General Public License version 2
  * or later (GPLv2+) WITHOUT ANY WARRANTY.
  */
 
 #include <crm_internal.h>
 
 #include <crm/common/unittest_internal.h>
 
 #include <limits.h>
 
 static void
 readable_interval(void **state)
 {
     assert_string_equal(pcmk__readable_interval(0), "0s");
+    assert_string_equal(pcmk__readable_interval(503), "503ms");
+    assert_string_equal(pcmk__readable_interval(3333), "3.333s");
     assert_string_equal(pcmk__readable_interval(30000), "30s");
+    assert_string_equal(pcmk__readable_interval(61000), "1m1s");
     assert_string_equal(pcmk__readable_interval(150000), "2m30s");
-    assert_string_equal(pcmk__readable_interval(3333), "3.333s");
     assert_string_equal(pcmk__readable_interval(UINT_MAX), "49d17h2m47.295s");
 }
 
 PCMK__UNIT_TEST(NULL, NULL,
                 cmocka_unit_test(readable_interval))