diff --git a/ChangeLog b/ChangeLog
index ef178c27f1..093b56f723 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Oct 18 23:01:32 2003  WATANABE Hirofumi  <eban@ruby-lang.org>
+
+	* missing/acosh.c (DBL_MANT_DIG): typo fix(ifdef -> ifndef).
+
 Sat Oct 18 05:48:59 2003  why the lucky stiff  <ruby-cvs@whytheluckystiff.net>
 
 	* ext/syck/rubyext.c: YAML::Syck::compile method.
diff --git a/missing/acosh.c b/missing/acosh.c
index 6a9daffa5f..a4443e191f 100644
--- a/missing/acosh.c
+++ b/missing/acosh.c
@@ -15,7 +15,7 @@
 #include <math.h>
 
 /* DBL_MANT_DIG must be less than 4 times of bits of int */
-#ifdef DBL_MANT_DIG
+#ifndef DBL_MANT_DIG
 #define DBL_MANT_DIG 53		/* in this case, at least 12 digit precision */
 #endif
 #define BIG_CRITERIA_BIT (1<<DBL_MANT_DIG/2)