diff --git a/src/main/python/ttconv/time_code.py b/src/main/python/ttconv/time_code.py
index 6f6915b5..5915b411 100644
--- a/src/main/python/ttconv/time_code.py
+++ b/src/main/python/ttconv/time_code.py
@@ -97,12 +97,12 @@ def parse(time_code: str) -> ClockTime:
 
   @staticmethod
   def from_seconds(seconds: Union[float, Fraction]) -> ClockTime:
-    """Creates a time code from time offset in seconds"""
+    """Creates a time code from time offset in seconds (rounds to the closest millisecond)"""
 
     if seconds < 0:
       raise ValueError("Seconds must not be less than zero")
 
-    seconds = float(seconds)
+    seconds = round(seconds, 3)
 
     h = floor(seconds / 3600)
     m = floor(seconds / 60 % 60)
diff --git a/src/test/python/test_time_code.py b/src/test/python/test_time_code.py
index 7f6ffd86..64068514 100644
--- a/src/test/python/test_time_code.py
+++ b/src/test/python/test_time_code.py
@@ -66,5 +66,22 @@ def test_time_code(self):
     self.assertEqual("24:00:01,500", str(time_code))
     self.assertEqual(seconds, time_code.to_seconds())
 
+  def test_from_seconds_rounding_up(self):
+      seconds = Fraction(41039999,7500)
+      time_code = ClockTime.from_seconds(seconds)
+      self.assertEqual(time_code.get_hours(), 1)
+      self.assertEqual(time_code.get_minutes(), 31)
+      self.assertEqual(time_code.get_seconds(), 12)
+      self.assertEqual(time_code.get_milliseconds(), 0)
+
+
+  def test_from_seconds_rounding_down(self):
+      seconds = 5471.9994
+      time_code = ClockTime.from_seconds(seconds)
+      self.assertEqual(time_code.get_hours(), 1)
+      self.assertEqual(time_code.get_minutes(), 31)
+      self.assertEqual(time_code.get_seconds(), 11)
+      self.assertEqual(time_code.get_milliseconds(), 999)
+
 if __name__ == '__main__':
   unittest.main()
diff --git a/src/test/python/test_vtt_writer.py b/src/test/python/test_vtt_writer.py
index 9f07163d..8aec6d67 100644
--- a/src/test/python/test_vtt_writer.py
+++ b/src/test/python/test_vtt_writer.py
@@ -131,7 +131,7 @@ def test_position(self):
     expected_vtt="""WEBVTT
 
 1
-00:00:03.501 --> 00:00:12.000 line:90%,end
+00:00:03.500 --> 00:00:12.000 line:90%,end
 Only one or two short samples are needed
 to make sure the conversion basically works
 
@@ -177,7 +177,7 @@ def test_align(self):
     expected_vtt="""WEBVTT
 
 1
-00:00:03.501 --> 00:00:12.000 align:center
+00:00:03.500 --> 00:00:12.000 align:center
 Only one or two short samples are needed
 to make sure the conversion basically works
 
@@ -217,7 +217,7 @@ def test_cue_id(self):
 
     expected_vtt="""WEBVTT
 
-00:00:03.501 --> 00:00:12.000
+00:00:03.500 --> 00:00:12.000
 Only one or two short samples are needed
 to make sure the conversion basically works