diff --git a/lib/msun/src/k_sin.c b/lib/msun/src/k_sin.c
index 6db5849c4164..fe2a56c00e9d 100644
--- a/lib/msun/src/k_sin.c
+++ b/lib/msun/src/k_sin.c
@@ -16,14 +16,16 @@ static char rcsid[] = "$FreeBSD$";
 #endif
 
 /* __kernel_sin( x, y, iy)
- * kernel sin function on [-pi/4, pi/4], pi/4 ~ 0.7854
+ * kernel sin function on ~[-pi/4, pi/4] (except on -0), pi/4 ~ 0.7854
  * Input x is assumed to be bounded by ~pi/4 in magnitude.
  * Input y is the tail of x.
  * Input iy indicates whether y is 0. (if iy=0, y assume to be 0). 
  *
  * Algorithm
  *	1. Since sin(-x) = -sin(x), we need only to consider positive x. 
- *	2. if x < 2^-27 (hx<0x3e400000 0), return x with inexact if x!=0.
+ *	2. Callers must return sin(-0) = -0 without calling here since our
+ *	   odd polynomial is not evaluated in a way that preserves -0.
+ *	   Callers may do the optimization sin(x) ~ x for tiny x.
  *	3. sin(x) is approximated by a polynomial of degree 13 on
  *	   [0,pi/4]
  *		  	         3            13