Index: Modules/datetimemodule.c
===================================================================
--- Modules/datetimemodule.c	(révision 73867)
+++ Modules/datetimemodule.c	(copie de travail)
@@ -1365,18 +1365,20 @@
 	return buffer + x;
 }
 
-static void
+static char *
 isoformat_time(PyDateTime_DateTime *dt, char buffer[], int bufflen)
 {
+	int x;
 	int us = DATE_GET_MICROSECOND(dt);
 
-	PyOS_snprintf(buffer, bufflen,
+	x = PyOS_snprintf(buffer, bufflen,
 		      "%02d:%02d:%02d",	/* 8 characters */
 		      DATE_GET_HOUR(dt),
 		      DATE_GET_MINUTE(dt),
 		      DATE_GET_SECOND(dt));
 	if (us)
-		PyOS_snprintf(buffer + 8, bufflen - 8, ".%06d", us);
+		x += PyOS_snprintf(buffer + 8, bufflen - 8, ".%06d", us);
+	return buffer + x;
 }
 
 /* ---------------------------------------------------------------------------
@@ -4200,8 +4202,8 @@
 	cp = isoformat_date((PyDateTime_Date *)self, buffer, sizeof(buffer));
 	assert(cp != NULL);
 	*cp++ = sep;
-	isoformat_time(self, cp, sizeof(buffer) - (cp - buffer));
-	result = PyString_FromString(buffer);
+	cp = isoformat_time(self, cp, sizeof(buffer) - (cp - buffer));
+	result = PyString_FromStringAndSize(buffer, cp - buffer);
 	if (result == NULL || ! HASTZINFO(self))
 		return result;
 
Index: Lib/test/test_datetime.py
===================================================================
--- Lib/test/test_datetime.py	(révision 73867)
+++ Lib/test/test_datetime.py	(copie de travail)
@@ -1173,6 +1173,7 @@
         self.assertEqual(t.isoformat(),    "0002-03-02T04:05:01.000123")
         self.assertEqual(t.isoformat('T'), "0002-03-02T04:05:01.000123")
         self.assertEqual(t.isoformat(' '), "0002-03-02 04:05:01.000123")
+        self.assertEqual(t.isoformat('\x00'), "0002-03-02\x0004:05:01.000123")
         # str is ISO format with the separator forced to a blank.
         self.assertEqual(str(t), "0002-03-02 04:05:01.000123")