diff --git a/ChangeLog b/ChangeLog
index bb5127228e..b12b31c84a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Oct 10 20:35:27 2009  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* math.c (math_atanh): reverted r25279.
+
 Sat Oct 10 19:03:29 2009  Tanaka Akira  <akr@fsij.org>
 
 	* ext/curses/curses.c: use rb_thread_blocking_region to avoid
diff --git a/math.c b/math.c
index 630aa13baa..51caf35c5d 100644
--- a/math.c
+++ b/math.c
@@ -298,6 +298,7 @@ math_atanh(VALUE obj, VALUE x)
     d0 = RFLOAT_VALUE(x);
     d = atanh(d0);
     domain_check(d0, d, "atanh");
+    infinity_check(x, d, "atanh");
     return DBL2NUM(d);
 }