diff --git a/moto/swf/responses.py b/moto/swf/responses.py
index f7f937169..afa9f1903 100644
--- a/moto/swf/responses.py
+++ b/moto/swf/responses.py
@@ -22,6 +22,10 @@ class SWFResponse(BaseResponse):
         if not isinstance(parameter, int):
             raise SWFSerializationException(parameter)
 
+    def _check_float(self, parameter):
+        if not isinstance(parameter, float):
+            raise SWFSerializationException(parameter)
+
     def _check_none_or_string(self, parameter):
         if parameter is not None:
             self._check_string(parameter)
@@ -120,13 +124,13 @@ class SWFResponse(BaseResponse):
         if start_time_filter is None and close_time_filter is None:
             raise SWFValidationException('Must specify time filter')
         if start_time_filter:
-            self._check_int(start_time_filter['oldestDate'])
+            self._check_float(start_time_filter['oldestDate'])
             if 'latestDate' in start_time_filter:
-                self._check_int(start_time_filter['latestDate'])
+                self._check_float(start_time_filter['latestDate'])
         if close_time_filter:
-            self._check_int(close_time_filter['oldestDate'])
+            self._check_float(close_time_filter['oldestDate'])
             if 'latestDate' in close_time_filter:
-                self._check_int(close_time_filter['latestDate'])
+                self._check_float(close_time_filter['latestDate'])
         if tag_filter:
             self._check_string(tag_filter['tag'])
         if type_filter:
@@ -168,9 +172,9 @@ class SWFResponse(BaseResponse):
         self._check_exclusivity(executionFilter=execution_filter,
                                 typeFilter=type_filter,
                                 tagFilter=tag_filter)
-        self._check_int(start_time_filter['oldestDate'])
+        self._check_float(start_time_filter['oldestDate'])
         if 'latestDate' in start_time_filter:
-            self._check_int(start_time_filter['latestDate'])
+            self._check_float(start_time_filter['latestDate'])
         if tag_filter:
             self._check_string(tag_filter['tag'])
         if type_filter:
diff --git a/tests/test_swf/responses/test_workflow_executions.py b/tests/test_swf/responses/test_workflow_executions.py
index d353eeb98..8e311a22c 100644
--- a/tests/test_swf/responses/test_workflow_executions.py
+++ b/tests/test_swf/responses/test_workflow_executions.py
@@ -7,7 +7,7 @@ import sure  # noqa
 import tests.backport_assert_raises  # noqa
 
 from moto import mock_swf
-from moto.core.utils import iso_8601_datetime_with_milliseconds
+from moto.core.utils import unix_time
 
 
 # Utils
@@ -126,7 +126,7 @@ def test_list_open_workflow_executions():
                                       run_id=run_id)
 
     yesterday = datetime.now() - timedelta(days=1)
-    oldest_date = iso_8601_datetime_with_milliseconds(yesterday)
+    oldest_date = unix_time(yesterday)
     response = conn.list_open_workflow_executions('test-domain',
                                                   oldest_date,
                                                   workflow_id='test-workflow')
@@ -160,7 +160,7 @@ def test_list_closed_workflow_executions():
                                       run_id=run_id)
 
     yesterday = datetime.now() - timedelta(days=1)
-    oldest_date = iso_8601_datetime_with_milliseconds(yesterday)
+    oldest_date = unix_time(yesterday)
     response = conn.list_closed_workflow_executions(
         'test-domain',
         start_oldest_date=oldest_date,