diff --git a/ChangeLog b/ChangeLog
index 4dc19c24aa..7ef47235e1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Nov 14 01:52:59 2007  Tanaka Akira  <akr@fsij.org>
+
+	* missing/isinf.c (isinf): don't define is the macro is defined.
+
 Wed Nov 14 01:34:42 2007  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* numeric.c (round): fallback definition.
diff --git a/missing/isinf.c b/missing/isinf.c
index eecb3eb498..4aef51b213 100644
--- a/missing/isinf.c
+++ b/missing/isinf.c
@@ -27,11 +27,18 @@ isinf(double n)
 #include <ieeefp.h>
 #endif
 
+/* 
+ * isinf may be provided only as a macro.
+ * ex. HP-UX, Solaris 10
+ * http://www.gnu.org/software/automake/manual/autoconf/Function-Portability.html
+ */
+#ifndef isinf
 int
 isinf(double n)
 {
     return (!finite(n) && !isnan(n));
 }
+#endif
 
 #else