diff --git a/ChangeLog b/ChangeLog
index 1f346e0d30..df2fdc67cd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun May 16 11:39:15 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/missing.h (signbit): add missing prototype.
+
 Sun May 16 10:49:47 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/iconv/iconv.c (rb_iconv_sys_fail): fix number of arguments.
diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index e4ac07018f..883971cb25 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -159,6 +159,10 @@ RUBY_EXTERN size_t strlcpy(char *, const char*, size_t);
 RUBY_EXTERN size_t strlcat(char *, const char*, size_t);
 #endif
 
+#ifndef HAVE_SIGNBIT
+RUBY_EXTERN int signbit(double x);
+#endif
+
 #if defined(__cplusplus)
 #if 0
 { /* satisfy cc-mode */