diff --git a/glib/tests/gdatetime.c b/glib/tests/gdatetime.c
index d46f653ac..9e1acd097 100644
--- a/glib/tests/gdatetime.c
+++ b/glib/tests/gdatetime.c
@@ -2930,6 +2930,8 @@ test_posix_parse (void)
 {
   GTimeZone *tz;
   GDateTime *gdt1, *gdt2;
+  gint i1, i2;
+  const char *expect_id;
 
   /* Check that an unknown zone name falls back to UTC. */
   G_GNUC_BEGIN_IGNORE_DEPRECATIONS
@@ -2952,18 +2954,40 @@ test_posix_parse (void)
   g_time_zone_unref (tz);
 
 /* This fails rules_from_identifier on Unix (though not on Windows)
- * but passes anyway because PST8PDT is a zone name.
+ * but can pass anyway because PST8PDT is a legacy System V zone name.
  */
   tz = g_time_zone_new_identifier ("PST8PDT");
+  expect_id = "PST8PDT";
+
+#ifndef G_OS_WIN32
+  /* PST8PDT is in tzdata's "backward" set, packaged as tzdata-legacy and
+   * not always present in some OSs; fall back to the equivalent geographical
+   * name if the "backward" time zones are absent. */
+  if (tz == NULL)
+    {
+      g_test_message ("Legacy PST8PDT time zone not available, falling back");
+      tz = g_time_zone_new_identifier ("America/Los_Angeles");
+      expect_id = "America/Los_Angeles";
+    }
+#endif
+
   g_assert_nonnull (tz);
-  g_assert_cmpstr (g_time_zone_get_identifier (tz), ==, "PST8PDT");
-  g_assert_cmpstr (g_time_zone_get_abbreviation (tz, 0), ==, "PST");
-  g_assert_cmpint (g_time_zone_get_offset (tz, 0), ==, - 8 * 3600);
-  g_assert (!g_time_zone_is_dst (tz, 0));
-  g_assert_cmpstr (g_time_zone_get_abbreviation (tz, 1), ==, "PDT");
-  g_assert_cmpint (g_time_zone_get_offset (tz, 1), ==,- 7 * 3600);
-  g_assert (g_time_zone_is_dst (tz, 1));
+  g_assert_cmpstr (g_time_zone_get_identifier (tz), ==, expect_id);
+  /* a date in winter = non-DST */
+  gdt1 = g_date_time_new (tz, 2024, 1, 1, 0, 0, 0);
+  i1 = g_time_zone_find_interval (tz, G_TIME_TYPE_STANDARD, g_date_time_to_unix (gdt1));
+  /* a date in summer = DST */
+  gdt2 = g_date_time_new (tz, 2024, 7, 1, 0, 0, 0);
+  i2 = g_time_zone_find_interval (tz, G_TIME_TYPE_DAYLIGHT, g_date_time_to_unix (gdt2));
+  g_assert_cmpstr (g_time_zone_get_abbreviation (tz, i1), ==, "PST");
+  g_assert_cmpint (g_time_zone_get_offset (tz, i1), ==, - 8 * 3600);
+  g_assert (!g_time_zone_is_dst (tz, i1));
+  g_assert_cmpstr (g_time_zone_get_abbreviation (tz, i2), ==, "PDT");
+  g_assert_cmpint (g_time_zone_get_offset (tz, i2), ==,- 7 * 3600);
+  g_assert (g_time_zone_is_dst (tz, i2));
   g_time_zone_unref (tz);
+  g_date_time_unref (gdt1);
+  g_date_time_unref (gdt2);
 
   tz = g_time_zone_new_identifier ("PST8PDT6:32:15");
 #ifdef G_OS_WIN32