diff --git a/lib/common/tests/iso8601/Makefile.am b/lib/common/tests/iso8601/Makefile.am
index 5135f4706b..8a9b581c31 100644
--- a/lib/common/tests/iso8601/Makefile.am
+++ b/lib/common/tests/iso8601/Makefile.am
@@ -1,19 +1,20 @@
 #
 # Copyright 2020-2024 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 $(top_srcdir)/mk/tap.mk
 include $(top_srcdir)/mk/unittest.mk
 
 # Add "_test" to the end of all test program names to simplify .gitignore.
-check_PROGRAMS = pcmk__add_time_from_xml_test		\
+check_PROGRAMS = crm_time_parse_duration_test		\
+		 pcmk__add_time_from_xml_test		\
 		 pcmk__readable_interval_test		\
 		 pcmk__set_time_if_earlier_test		\
 		 pcmk__time_format_hr_test
 
 TESTS = $(check_PROGRAMS)
diff --git a/lib/common/tests/iso8601/crm_time_parse_duration_test.c b/lib/common/tests/iso8601/crm_time_parse_duration_test.c
new file mode 100644
index 0000000000..d614760bca
--- /dev/null
+++ b/lib/common/tests/iso8601/crm_time_parse_duration_test.c
@@ -0,0 +1,92 @@
+/*
+ * Copyright 2024 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 <crm/common/iso8601.h>
+#include "crmcommon_private.h"
+
+static void
+empty_arg(void **state)
+{
+    assert_null(crm_time_parse_duration(NULL));
+    assert_null(crm_time_parse_duration(""));
+}
+
+static void
+invalid_arg(void **state)
+{
+    // Valid except doesn't start with P
+    assert_null(crm_time_parse_duration("X3Y6M4DT12H30M5S"));
+
+    // Illegal character after P
+    assert_null(crm_time_parse_duration("P"));
+    assert_null(crm_time_parse_duration("P 3Y6M4DT12H30M5S"));
+    assert_null(crm_time_parse_duration("PX3Y6M4DT12H30M5S"));
+
+    // Integer overflow
+    assert_null(crm_time_parse_duration("P2147483648Y6M4DT12H30M5S"));
+    assert_null(crm_time_parse_duration("P3Y2147483648M4DT12H30M5S"));
+    assert_null(crm_time_parse_duration("P3Y6M2147483648DT12H30M5S"));
+    assert_null(crm_time_parse_duration("P3Y6M4DT2147483648H30M5S"));
+    assert_null(crm_time_parse_duration("P3Y6M4DT12H2147483648M5S"));
+    assert_null(crm_time_parse_duration("P3Y6M4DT12H30MP2147483648S"));
+
+    // Missing or invalid units
+    assert_null(crm_time_parse_duration("P3Y6M4DT12H30M5"));
+    assert_null(crm_time_parse_duration("P3Y6M4DT12H30M5X"));
+    assert_null(crm_time_parse_duration("P3X6M4DT12H30M5S"));
+    assert_null(crm_time_parse_duration("PT"));
+    assert_null(crm_time_parse_duration("P/"));
+
+#if 0
+    // @TODO The current implementation treats these as valid
+
+    // Units out of order
+    assert_null(crm_time_parse_duration("P6M3Y4DT12H30M5S"));
+    assert_null(crm_time_parse_duration("P6M3DT12HY430M5S"));
+
+    // Same unit specified multiple times
+    assert_null(crm_time_parse_duration("P6Y4M3D1MT12H30M5S"));
+
+    // Weeks mixed with other units
+    assert_null(crm_time_parse_duration("P6Y4M3W3D1MT12H30M5S"));
+    assert_null(crm_time_parse_duration("P3WT12H30M5S"));
+#endif
+}
+
+static void
+valid_arg(void **state)
+{
+    // @TODO Check result value
+    assert_non_null(crm_time_parse_duration("P3Y6M4DT12H30M5S"));
+    assert_non_null(crm_time_parse_duration("P3Y6M4DT12H30M"));
+    assert_non_null(crm_time_parse_duration("P3Y6M4D"));
+    assert_non_null(crm_time_parse_duration("P1M"));  // 1 month
+    assert_non_null(crm_time_parse_duration("PT1M")); // 1 minute
+    assert_non_null(crm_time_parse_duration("P7W"));
+
+#if 0
+    // @TODO Current implementation can't handle these cases
+
+    // Fractional value for last unit
+    assert_non_null(crm_time_parse_duration("P3Y6M4DT12H30.5M"));
+    assert_non_null(crm_time_parse_duration("P3Y6M4DT12H30,5M"));
+
+    // P<YYYY>-<MM>-<DD>T<hh>:<mm>:<ss> format
+    assert_non_null(crm_time_parse_duration("P0003-02-01T11:10:09");
+#endif
+}
+
+PCMK__UNIT_TEST(NULL, NULL,
+                cmocka_unit_test(empty_arg),
+                cmocka_unit_test(invalid_arg),
+                cmocka_unit_test(valid_arg));