diff --git a/usr.sbin/iostat/iostat.8 b/usr.sbin/iostat/iostat.8
index 595220966216..c8427e633b3e 100644
--- a/usr.sbin/iostat/iostat.8
+++ b/usr.sbin/iostat/iostat.8
@@ -241,7 +241,14 @@ If no repeat
 is specified, the default is infinity.
 The
 .Nm
-command will accept and honor a non-integer number of seconds.
+command will accept and honor a non-integer number of seconds.  Note that
+the interval only has millisecond granularity.  Smaller values will be 
+truncated.
+.Pp
+e.g. -w1.0001 becomes -w1.000
+.Pp
+The interval will also suffer from modifications to hz so your mileage
+may vary.
 .It Fl x
 Show extended disk statistics.
 Each disk is displayed on a line of its own with all available statistics.