diff --git a/gallery_dl/dt.py b/gallery_dl/dt.py
index 74e65fe3..b37ebf38 100644
--- a/gallery_dl/dt.py
+++ b/gallery_dl/dt.py
@@ -22,7 +22,7 @@ class NullDatetime(datetime):
         return "[Invalid DateTime]"
 
     def __format__(self, format_spec):
-        return f"[Invalid DateTime {format_spec}]"
+        return "[Invalid DateTime]"
 
 
 NONE = NullDatetime(1, 1, 1)
diff --git a/test/test_formatter.py b/test/test_formatter.py
index e4444346..f08ae49c 100644
--- a/test/test_formatter.py
+++ b/test/test_formatter.py
@@ -15,7 +15,7 @@ import datetime
 import tempfile
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
-from gallery_dl import formatter, text, util, config  # noqa E402
+from gallery_dl import formatter, text, dt, util, config  # noqa E402
 
 try:
     import jinja2
@@ -154,7 +154,7 @@ class TestFormatter(unittest.TestCase):
         self._run_test("{t}" , self.kwdict["t"] , None, int)
         self._run_test("{t}" , self.kwdict["t"] , None, util.identity)
         self._run_test("{dt}", self.kwdict["dt"], None, util.identity)
-        self._run_test("{ds}", self.kwdict["dt"], None, text.parse_datetime)
+        self._run_test("{ds}", self.kwdict["dt"], None, dt.parse_iso)
         self._run_test("{ds:D%Y-%m-%dT%H:%M:%S%z}", self.kwdict["dt"],
                        None, util.identity)
 
@@ -271,8 +271,8 @@ class TestFormatter(unittest.TestCase):
 
     def test_specifier_datetime(self):
         self._run_test("{ds:D%Y-%m-%dT%H:%M:%S%z}", "2010-01-01 00:00:00")
-        self._run_test("{ds:D%Y}", "0101-01-01 00:00:00")
-        self._run_test("{l2:D%Y}", "0101-01-01 00:00:00")
+        self._run_test("{ds:D%Y}", "[Invalid DateTime]")
+        self._run_test("{l2:D%Y}", "[Invalid DateTime]")
 
     def test_specifier_offset(self):
         self._run_test("{dt:O 01:00}", "2010-01-01 01:00:00")