diff --git a/ChangeLog b/ChangeLog
index 568a02d956..c4ce9f34c8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Apr  4 22:32:32 2013  Tanaka Akira  <akr@fsij.org>
+
+	* time.c (time_strftime): Describe %L and %N truncates digits under
+	  the specified length.
+	  [ruby-core:52130] [Bug #7829]
+
 Thu Apr  4 22:08:46 2013  Tanaka Akira  <akr@fsij.org>
 
 	* object.c (rb_mod_cvar_set): Reverted "avoid inadvertent
diff --git a/time.c b/time.c
index ce3be371cc..e9f59c7353 100644
--- a/time.c
+++ b/time.c
@@ -4455,6 +4455,7 @@ strftimev(const char *fmt, VALUE time, rb_encoding *enc)
  *      %S - Second of the minute (00..60)
  *
  *      %L - Millisecond of the second (000..999)
+ *           The digits under millisecond are truncated to not produce 1000.
  *      %N - Fractional seconds digits, default is 9 digits (nanosecond)
  *              %3N  milli second (3 digits)
  *              %6N  micro second (6 digits)
@@ -4464,6 +4465,8 @@ strftimev(const char *fmt, VALUE time, rb_encoding *enc)
  *              %18N atto second (18 digits)
  *              %21N zepto second (21 digits)
  *              %24N yocto second (24 digits)
+ *           The digits under the specified length are truncated to avoid
+ *           carry up.
  *
  *    Time zone:
  *      %z - Time zone as hour and minute offset from UTC (e.g. +0900)