diff --git a/src/library/flatten.py b/src/library/flatten.py
index f6ef1d7..b8bafb2 100644
--- a/src/library/flatten.py
+++ b/src/library/flatten.py
@@ -114,7 +114,7 @@ def _add_to_output(self, canonical_name, value, output):
         # Date time?
         if [x for x in self.CANONICAL_NAMES_WITH_DATE_TIMES if x in canonical_name]:
             try:
-                dt_object = dateutil.parser.parse(value)
+                dt_object = utils.parse_xsd_date_value(value) or dateutil.parser.parse(value)
                 if dt_object:
                     # This mirrors output of old flaterrer system
                     value = dt_object.strftime("%Y-%m-%dT%H:%M:%S.%f")[:-3]+"Z"
diff --git a/src/library/utils.py b/src/library/utils.py
index 6958700..82bf7c1 100644
--- a/src/library/utils.py
+++ b/src/library/utils.py
@@ -1,6 +1,8 @@
 import chardet
 from library.logger import getLogger
 import hashlib
+import re
+import datetime
 
 logger = getLogger("utils")
 
@@ -45,3 +47,64 @@ def get_hash_for_identifier(id):
 def chunk_list(l, n):
     for i in range(0, n):
         yield l[i::n]
+
+
+class TimeZoneFixedOffset(datetime.tzinfo):
+    def __init__(self, hours, mins):
+        self.hours = hours
+        self.mins = mins
+
+    def utcoffset(self, dt):
+        if self.hours > 0:
+            return datetime.timedelta(hours=self.hours, minutes=self.mins)
+        else:
+            return datetime.timedelta(hours=self.hours, minutes=(0-self.mins))
+
+    def tzname(self, dt):
+        return "UTC{hours:+02d}:{mins:02d}".format(hours=self.hours, mins=self.mins)
+
+    def dst(self, dt):
+        return datetime.timedelta(0)
+
+
+def parse_xsd_date_value(in_str):
+    """
+    Takes in a string that may be a valid xsd:date value
+
+    Returns a datetime object if it is (None is if it is not)
+
+    Years larger than 9999 should work but Python won't let us.
+    See https://www.w3.org/TR/xmlschema-2/#date section 3.2.9.1 leading to section 3.2.7.1
+    """
+    # Date only
+    try:
+        v = datetime.datetime.strptime(in_str, "%Y-%m-%d")
+        if v:
+            return v
+    except ValueError:
+        pass
+    # Date and Z time zone
+    try:
+        v = datetime.datetime.strptime(in_str, "%Y-%m-%dZ")
+        if v:
+            return v
+    except ValueError:
+        pass
+    # Date and plus minus time zone
+    # We can't use %z as that works with -/+0000
+    # and https://www.w3.org/TR/xmlschema-2/#dateTime section 3.2.7.3 defines -/+00:00
+    try:
+        match = re.search(r'^(\d\d\d\d)-(\d\d)-(\d\d)(\-|\+)(\d\d):(\d\d)$', in_str)
+        if match:
+            tzinfo = TimeZoneFixedOffset(
+                int(match.group(5)) if match.group(4) == '+' else 0 - int(match.group(5)),
+                int(match.group(6))
+            )
+            dt = datetime.datetime(int(match.group(1)), int(match.group(2)), int(match.group(3)), tzinfo=tzinfo)
+            # We ignore the time zone part for now
+            return dt
+    except ValueError:
+        pass
+    # We fail
+    return None
+
diff --git a/src/tests/fixtures_flatten_flatterer/bad_dates.expected.json b/src/tests/fixtures_flatten_flatterer/bad_dates.expected.json
index 80c20a1..f149763 100644
--- a/src/tests/fixtures_flatten_flatterer/bad_dates.expected.json
+++ b/src/tests/fixtures_flatten_flatterer/bad_dates.expected.json
@@ -1,14 +1,17 @@
 [
   {
-    "dataset_version": "",
-    "iati_identifier": "ACT-1"
+    "dataset_version": "2.03",
+    "iati_identifier": "big-year",
+    "activity_date_type": "1"
   },
   {
-    "dataset_version": "",
-    "iati_identifier": "ACT-2"
+    "dataset_version": "2.03",
+    "iati_identifier": "rubbish-1",
+    "activity_date_type": "1"
   },
   {
-    "dataset_version": "",
-    "iati_identifier": "ACT-3"
+    "dataset_version": "2.03",
+    "iati_identifier": "rubbish-2",
+    "activity_date_type": "1"
   }
 ]
diff --git a/src/tests/fixtures_flatten_flatterer/bad_dates.input.xml b/src/tests/fixtures_flatten_flatterer/bad_dates.input.xml
index fdaa9af..5e51ac9 100644
--- a/src/tests/fixtures_flatten_flatterer/bad_dates.input.xml
+++ b/src/tests/fixtures_flatten_flatterer/bad_dates.input.xml
@@ -1,11 +1,17 @@
-<iati-activities>
+<iati-activities version="2.03">
+    <!-- last-updated-datetime is xsd:dateTime. activity-date iso-date is xsd:date - test separately in case parsing is different! -->
+    <!-- test case - actually years bigger than 10000 should be allowed but Python won't let us. Don't crash. -->
     <iati-activity last-updated-datetime="12021-11-05">
-        <iati-identifier>ACT-1</iati-identifier>
+        <iati-identifier>big-year</iati-identifier>
+        <activity-date iso-date="12021-11-05" type="1" />
     </iati-activity>
-    <iati-activity last-updated-datetime="2006-04-23+09:00">
-        <iati-identifier>ACT-2</iati-identifier>
+    <!-- test case - various rubbish won't crash -->
+    <iati-activity last-updated-datetime="cat">
+        <iati-identifier>rubbish-1</iati-identifier>
+        <activity-date iso-date="cat" type="1" />
     </iati-activity>
-    <iati-activity last-updated-datetime="2010-01-01Z">
-        <iati-identifier>ACT-3</iati-identifier>
+    <iati-activity last-updated-datetime="2023-15-40">
+        <iati-identifier>rubbish-2</iati-identifier>
+        <activity-date iso-date="2023-15-40" type="1" />
     </iati-activity>
 </iati-activities>
diff --git a/src/tests/fixtures_flatten_flatterer/date_format_timezones.expected.json b/src/tests/fixtures_flatten_flatterer/date_format_timezones.expected.json
index 1a03725..a23b035 100644
--- a/src/tests/fixtures_flatten_flatterer/date_format_timezones.expected.json
+++ b/src/tests/fixtures_flatten_flatterer/date_format_timezones.expected.json
@@ -1,7 +1,12 @@
 [
-    {
-        "dataset_version": "2.03",
-        "iati_identifier": "ACT-1",
-        "last_updated_datetime": "2023-07-17T08:05:08.160Z"
-    }
+  {
+    "dataset_version": "2.03",
+    "last_updated_datetime": "2023-07-17T08:05:08.160Z",
+    "iati_identifier": "ACT-1"
+  },
+  {
+    "dataset_version": "2.03",
+    "last_updated_datetime": "2023-07-17T00:00:00.000Z",
+    "iati_identifier": "ACT-2"
+  }
 ]
diff --git a/src/tests/fixtures_flatten_flatterer/date_format_timezones.input.xml b/src/tests/fixtures_flatten_flatterer/date_format_timezones.input.xml
index a5bedcc..37aa991 100644
--- a/src/tests/fixtures_flatten_flatterer/date_format_timezones.input.xml
+++ b/src/tests/fixtures_flatten_flatterer/date_format_timezones.input.xml
@@ -2,4 +2,7 @@
     <iati-activity last-updated-datetime="2023-07-17T08:05:08.160000+00:00">
         <iati-identifier>ACT-1</iati-identifier>
     </iati-activity>
+    <iati-activity last-updated-datetime="2023-07-17+00:00">
+        <iati-identifier>ACT-2</iati-identifier>
+    </iati-activity>
 </iati-activities>
diff --git a/src/tests/test_utils.py b/src/tests/test_utils.py
index 1b93f12..fbf8ed1 100644
--- a/src/tests/test_utils.py
+++ b/src/tests/test_utils.py
@@ -1,5 +1,46 @@
-from library.utils import get_hash_for_identifier
+from library.utils import get_hash_for_identifier, parse_xsd_date_value
+import pytest
 
 def test_get_hash_for_identifier_1():
     assert "9d989e8d27dc9e0ec3389fc855f142c3d40f0c50" == get_hash_for_identifier("cat")
 
+PARSE_XSD_DATE_VALUE = [
+    # just nonsense
+    ('cat', None),
+    # dates only
+    ('2023-11-15', '2023-11-15T00:00:00'),
+    # dates only ... that aren't valid
+    ('2023-13-15', None),
+    ('2023-00-15', None),
+    ('2023-01-32', None),
+    ('2023-02-30', None),
+    # dates and Z time zones
+    ('2023-11-15Z', '2023-11-15T00:00:00'),
+    # dates and Z time zones ... that aren't valid
+    ('2023-13-15Z', None),
+    ('2023-00-15Z', None),
+    ('2023-01-32Z', None),
+    ('2023-02-30Z', None),
+    # dates and offset time zones
+    ('2023-11-15+00:00', '2023-11-15T00:00:00+00:00'),
+    ('2023-11-15+01:00', '2023-11-15T00:00:00+01:00'),
+    ('2023-11-15+01:30', '2023-11-15T00:00:00+01:30'),
+    ('2023-11-15-00:00', '2023-11-15T00:00:00+00:00'),
+    ('2023-11-15-01:00', '2023-11-15T00:00:00-01:00'),
+    ('2023-11-15-01:30', '2023-11-15T00:00:00-01:30'),
+    # dates and offset time zones ... that aren't valid
+    ('2023-13-15-00:00', None),
+    ('2023-00-15-00:00', None),
+    ('2023-01-32-00:00', None),
+    ('2023-02-30-00:00', None),
+    # This should be valid in xsd:date but python can't handle years bigger than 9999
+    ('10000-01-01', None),
+]
+
+@pytest.mark.parametrize("in_value, expected_value", PARSE_XSD_DATE_VALUE)
+def test_parse_xsd_date_value(in_value, expected_value):
+    actual = parse_xsd_date_value(in_value)
+    if expected_value:
+        assert actual.isoformat() == expected_value
+    else:
+        assert actual is None