diff --git a/glib/gdatetime.c b/glib/gdatetime.c
index 142338128..0ec390c94 100644
--- a/glib/gdatetime.c
+++ b/glib/gdatetime.c
@@ -3492,12 +3492,12 @@ g_date_time_format_iso8601 (GDateTime *datetime)
   GString *outstr = NULL;
   gchar *main_date = NULL;
   gint64 offset;
-  gchar *format = "%Y-%m-%dT%H:%M:%S";
+  gchar *format = "%C%y-%m-%dT%H:%M:%S";
 
   /* if datetime has sub-second non-zero values below the second precision we
    * should print them as well */
   if (datetime->usec % G_TIME_SPAN_SECOND != 0)
-    format = "%Y-%m-%dT%H:%M:%S.%f";
+    format = "%C%y-%m-%dT%H:%M:%S.%f";
 
   /* Main date and time. */
   main_date = g_date_time_format (datetime, format);
diff --git a/glib/tests/gdatetime.c b/glib/tests/gdatetime.c
index 2853b1174..141263b66 100644
--- a/glib/tests/gdatetime.c
+++ b/glib/tests/gdatetime.c
@@ -2321,6 +2321,22 @@ test_format_iso8601 (void)
   g_free (p);
   g_date_time_unref (dt);
   g_time_zone_unref (tz);
+
+  tz = g_time_zone_new_utc ();
+  dt = g_date_time_new (tz, 9, 1, 2, 3, 4, 55);
+  p = g_date_time_format_iso8601 (dt);
+  g_assert_cmpstr (p, ==, "0009-01-02T03:04:55Z");
+  g_free (p);
+  g_date_time_unref (dt);
+  g_time_zone_unref (tz);
+
+  tz = g_time_zone_new_utc ();
+  dt = g_date_time_new (tz, 9990, 1, 2, 3, 4, 55.000001);
+  p = g_date_time_format_iso8601 (dt);
+  g_assert_cmpstr (p, ==, "9990-01-02T03:04:55.000001Z");
+  g_free (p);
+  g_date_time_unref (dt);
+  g_time_zone_unref (tz);
 }
 
 typedef struct