diff --git a/pysnooper/pycompat.py b/pysnooper/pycompat.py
index 1899ff8..c6b23b3 100644
--- a/pysnooper/pycompat.py
+++ b/pysnooper/pycompat.py
@@ -90,9 +90,6 @@ else:
         return datetime_module.time(hour, minute, second, microsecond)
 
 
-def timedelta_isoformat(timedelta, timespec='microseconds'):
-    assert isinstance(timedelta, datetime_module.timedelta)
-    if timespec != 'microseconds':
-        raise NotImplementedError
+def timedelta_isoformat(timedelta):
     time = (datetime_module.datetime.min + timedelta).time()
-    return time_isoformat(time, timespec)
+    return time_isoformat(time)
diff --git a/pysnooper/tracer.py b/pysnooper/tracer.py
index c7d6e49..1c9103b 100644
--- a/pysnooper/tracer.py
+++ b/pysnooper/tracer.py
@@ -368,7 +368,7 @@ class Tracer:
         if self.elapsed_time:
             duration = datetime_module.datetime.now() - self.start_times[-1]
             now_string = pycompat.timedelta_isoformat(
-                duration, timespec='microseconds') if not self.normalize else ' ' * 15
+                duration) if not self.normalize else ' ' * 15
         else:
             now = datetime_module.datetime.now().time()
             now_string = pycompat.time_isoformat(now, timespec='microseconds') if not self.normalize else ' ' * 15