diff --git a/pysnooper/pycompat.py b/pysnooper/pycompat.py
index ce7566e..5b9a481 100644
--- a/pysnooper/pycompat.py
+++ b/pysnooper/pycompat.py
@@ -6,6 +6,7 @@ import abc
 import os
 import inspect
 import sys
+import datetime as datetime_module
 
 PY3 = (sys.version_info[0] == 3)
 PY2 = not PY3
@@ -64,3 +65,18 @@ try:
     from collections import abc as collections_abc
 except ImportError: # Python 2.7
     import collections as collections_abc
+
+if sys.version_info[:2] >= (3, 6):
+    time_isoformat = datetime_module.time.isoformat
+else:
+    def time_isoformat(time, timespec='microseconds'):
+        assert isinstance(time, datetime_module.time)
+        if timespec != 'microseconds':
+            raise NotImplementedError
+        result = '{:02d}:{:02d}:{:02d}.{:06d}'.format(
+            time.hour, time.minute, time.second, time.microsecond
+        )
+        assert len(result) == 15
+        return result
+
+
diff --git a/pysnooper/tracer.py b/pysnooper/tracer.py
index b1b1a16..c62da1b 100644
--- a/pysnooper/tracer.py
+++ b/pysnooper/tracer.py
@@ -346,7 +346,8 @@ class Tracer:
         #                                                                     #
         ### Finished checking whether we should trace this line. ##############
 
-        now_string = datetime_module.datetime.now().time().isoformat()
+        now = datetime_module.datetime.now().time()
+        now_string = pycompat.time_isoformat(now, timespec='microseconds')
         line_no = frame.f_lineno
         source_path, source = get_path_and_source_from_frame(frame)
         if self.last_source_path != source_path: