diff --git a/ChangeLog b/ChangeLog
index 1c166c1106..22b4a3177e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Fri Jun  3 20:56:40 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* include/ruby/missing.h, numeric.c (round): moved prototype of round()
+	  from numeric.c to missing.h.  (note: round() is C99 feature, so ruby
+	  provides it if not exists in C runtime.)
+
 Fri Jun  3 19:58:14 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* io.c (io_fflush): windows -- call fsync() only when the FD is tied to
diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index 7cb2d9233c..1a1aa958ac 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -80,6 +80,10 @@ RUBY_EXTERN int dup2(int, int);
 RUBY_EXTERN int eaccess(const char*, int);
 #endif
 
+#ifndef HAVE_ROUND
+RUBY_EXTERN double round(double);	/* numeric.c */
+#endif
+
 #ifndef HAVE_FINITE
 RUBY_EXTERN int finite(double);
 #endif
diff --git a/numeric.c b/numeric.c
index 0c419e1be7..95dc7bbab4 100644
--- a/numeric.c
+++ b/numeric.c
@@ -78,8 +78,6 @@ const unsigned char rb_nan[] = "\x00\x00\xc0\x7f";
 const unsigned char rb_nan[] = "\x7f\xc0\x00\x00";
 #endif
 
-extern double round(double);
-
 #ifndef HAVE_ROUND
 double
 round(double x)