diff --git a/dapr/serializers/util.py b/dapr/serializers/util.py
index 522ad03d3..deb4f34d2 100644
--- a/dapr/serializers/util.py
+++ b/dapr/serializers/util.py
@@ -74,4 +74,7 @@ def convert_to_dapr_duration(td: timedelta) -> str:
     milliseconds, microseconds = divmod(td.microseconds, 1000.0)
     hours, mins = divmod(total_minutes, 60.0)
 
-    return f'{hours:.0f}h{mins:.0f}m{seconds:.0f}s{milliseconds:.0f}ms{microseconds:.0f}μs'
+    # `seconds` still carries the sub-second fraction, which is also emitted via
+    # the ms/μs fields below; truncate it so the fraction is not double-counted
+    # (and so a fraction >= 0.5 is not rounded up into an extra whole second).
+    return f'{hours:.0f}h{mins:.0f}m{int(seconds)}s{milliseconds:.0f}ms{microseconds:.0f}μs'
diff --git a/tests/serializers/test_util.py b/tests/serializers/test_util.py
index 25124fdf6..07ce8a2ae 100644
--- a/tests/serializers/test_util.py
+++ b/tests/serializers/test_util.py
@@ -63,6 +63,13 @@ def test_convert_timedelta_to_dapr_duration(self):
         )
         self.assertEqual(duration, '4h15m40s123ms35μs')
 
+    def test_convert_timedelta_to_dapr_duration_subsecond(self):
+        # A sub-second fraction >= 0.5 must not be rounded up into an extra whole
+        # second nor double-counted with the ms/μs fields; the round-trip must be exact.
+        duration = convert_to_dapr_duration(timedelta(milliseconds=1500))
+        self.assertEqual(duration, '0h0m1s500ms0μs')
+        self.assertEqual(convert_from_dapr_duration(duration), timedelta(milliseconds=1500))
+
     def test_convert_invalid_duration_string(self):
         TESTSTRING = '4h15m40s123ms35μshello'
         with self.assertRaises(ValueError) as exeception_context: