diff --git a/pysnooper/pycompat.py b/pysnooper/pycompat.py
index c6b23b3..fedb3a5 100644
--- a/pysnooper/pycompat.py
+++ b/pysnooper/pycompat.py
@@ -90,6 +90,6 @@ else:
         return datetime_module.time(hour, minute, second, microsecond)
 
 
-def timedelta_isoformat(timedelta):
+def timedelta_isoformat(timedelta, timespec='microseconds'):
     time = (datetime_module.datetime.min + timedelta).time()
-    return time_isoformat(time)
+    return time_isoformat(time, timespec)
diff --git a/pysnooper/tracer.py b/pysnooper/tracer.py
index e6a4a65..7a56d3b 100644
--- a/pysnooper/tracer.py
+++ b/pysnooper/tracer.py
@@ -374,7 +374,7 @@ class Tracer:
                 start_time = self.start_times[frame]
             duration = datetime_module.datetime.now() - start_time
             now_string = pycompat.timedelta_isoformat(
-                duration) if not self.normalize else ' ' * 15
+                duration, timespec='microseconds') 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