diff --git a/ChangeLog b/ChangeLog
index f00f4d796c..87774c7b89 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Jul 10 14:42:02 2003  WATANABE Hirofumi  <eban@ruby-lang.org>
+
+	* math.c (math_log): nan takes a dummy argument on Cygwin 1.5.0.
+
 Wed Jul  9 23:50:46 2003  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
 
 	* regex.c (mbctab_sjis): 0x80 is not shift jis first byte.
diff --git a/math.c b/math.c
index 8d7bd8c53f..5268598750 100644
--- a/math.c
+++ b/math.c
@@ -193,8 +193,12 @@ math_exp(obj, x)
 }
 
 #if defined __CYGWIN__
-#define log(x) ((x) < 0.0 ? nan() : log(x))
-#define log10(x) ((x) < 0.0 ? nan() : log10(x))
+# include <cygwin/version.h>
+# if CYGWIN_VERSION_DLL_MAJOR < 1005
+#  define nan(x) nan()
+# endif
+# define log(x) ((x) < 0.0 ? nan("") : log(x))
+# define log10(x) ((x) < 0.0 ? nan("") : log10(x))
 #endif
 
 static VALUE