diff --git a/ChangeLog b/ChangeLog
index fc9e4fd52e..8914c41584 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Thu Feb 18 22:31:15 2010  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* math.c (math_atanh): raise ERANGE without calling atanh if absolute
+	  value is 1 to achieve platform-independent math.  [ruby-core:28219]
+
+	* math.c (math_lgamma): return [Infinity, 1] without calling lgamma_r
+	  if argument is infinity or -infinity.  [ruby-core:28219]
+
 Thu Feb 18 22:28:00 2010  Kenta Murata  <mrkn@mrkn.jp>
 
 	* confiure.in: new --with-ext and --with-out-ext options for extmk.
diff --git a/math.c b/math.c
index 027932dee9..51a89c3f55 100644
--- a/math.c
+++ b/math.c
@@ -310,6 +310,10 @@ math_atanh(VALUE obj, VALUE x)
     Need_Float(x);
     errno = 0;
     d0 = RFLOAT_VALUE(x);
+    if (d0 == 1.0 || d0 == -1.0) {
+	errno = ERANGE;
+	rb_sys_fail("atanh");
+    }
     d = atanh(d0);
     domain_check(d0, d, "atanh");
     infinity_check(x, d, "atanh");
@@ -715,6 +719,9 @@ math_lgamma(VALUE obj, VALUE x)
     Need_Float(x);
     errno = 0;
     d0 = RFLOAT_VALUE(x);
+    if (isinf(d0)) {
+	return rb_assoc_new(DBL2NUM(INFINITY), INT2FIX(1));
+    }
     d = lgamma_r(d0, &sign);
     domain_check(d0, d, "lgamma");
     v = DBL2NUM(d);