diff --git a/src/flask_moment/__init__.py b/src/flask_moment/__init__.py
index 08edaf5..98b52b9 100644
--- a/src/flask_moment/__init__.py
+++ b/src/flask_moment/__init__.py
@@ -48,7 +48,8 @@
 class moment(object):
     """Create a moment object.
 
-    :param timestamp: The ``datetime`` object representing the timestamp.
+    :param timestamp: The ``datetime`` object or ISO 8601 string representing
+                      the timestamp.
     :param local: If ``True``, the ``timestamp`` argument is given in the
                   local client time. In most cases this argument will be set
                   to ``False`` and all the timestamps managed by the server
@@ -176,6 +177,8 @@ def __init__(self, timestamp=None, local=False):
         self.local = local
 
     def _timestamp_as_iso_8601(self, timestamp):
+        if isinstance(timestamp, str):
+            return timestamp  # assume it is already in ISO 8601 format
         tz = ''
         if not self.local:
             tz = 'Z'
@@ -235,7 +238,7 @@ def fromTime(self, timestamp, no_suffix=False, refresh=False):
 
         This function maps to the ``from()`` function from moment.js.
 
-        :param timestamp: The reference ``datetime`` object.
+        :param timestamp: The reference ``datetime`` object or ISO 8601 string.
         :param no_suffix: if set to ``True``, the time difference does not
                           include the suffix (the "ago" or similar).
         :param refresh: If set to ``True``, refresh the timestamp at one
@@ -268,7 +271,7 @@ def toTime(self, timestamp, no_suffix=False, refresh=False):
 
         This function maps to the ``to()`` function from moment.js.
 
-        :param timestamp: The reference ``datetime`` object.
+        :param timestamp: The reference ``datetime`` object or ISO 8601 string.
         :param no_suffix: if set to ``True``, the time difference does not
                           include the suffix (the "ago" or similar).
         :param refresh: If set to ``True``, refresh the timestamp at one
@@ -321,7 +324,7 @@ def diff(self, timestamp, units, refresh=False):
         """Render the difference between the moment object and the given
         timestamp using the provided units.
 
-        :param timestamp: The reference ``datetime`` object.
+        :param timestamp: The reference ``datetime`` object or ISO 8601 string.
         :param units: A time unit such as `years`, `months`, `weeks`, `days`,
                       `hours`, `minutes` or `seconds`.
         :param refresh: If set to ``True``, refresh the timestamp at one
diff --git a/tests/test_flask_moment.py b/tests/test_flask_moment.py
index 02fefd0..4dc0eee 100644
--- a/tests/test_flask_moment.py
+++ b/tests/test_flask_moment.py
@@ -96,12 +96,18 @@ def test_flask_moment_js(self):
         assert isinstance(js, str)
         assert 'function flask_moment_render(elem) {' in js
 
-    def test__moment_timestamp_passed(self):
+    def test__moment_datetime_passed(self):
         ts = datetime(2017, 1, 15, 22, 47, 6, 479898)
         m = self.moment(timestamp=ts)
         assert m.timestamp == ts
         assert m.local is False
 
+    def test__moment_iso8601_passed(self):
+        ts = '2017-01-15T22:47:06.479898Z'
+        m = self.moment(timestamp=ts)
+        assert m.timestamp == ts
+        assert m.local is False
+
     @mock.patch('flask_moment.datetime')
     def test__timestamp_as_iso_8601_default(self, dt):
         dt.utcnow.return_value = datetime(2017, 1, 15, 22, 1, 21, 101361)
@@ -116,6 +122,11 @@ def test__timestamp_as_iso_8601_local_true(self, dt):
         ts = m._timestamp_as_iso_8601(timestamp=m.timestamp)
         assert ts == '2017-01-15T22:01:21'
 
+    def test__timestamp_as_iso_8601_string(self):
+        ts = '2017-01-15T22:47:06.479898Z'
+        m = self.moment(local=True)  # local is ignored in this case
+        assert m._timestamp_as_iso_8601(timestamp=ts) == ts
+
     def test__render_default(self):
         m = self.moment()
         rts = m._render(func='format')  # rts: rendered time stamp