diff --git a/ChangeLog b/ChangeLog
index 9dff90758b..97443227e8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Wed Jul 13 15:59:59 2016  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* math.c (_USE_MATH_DEFINES): it must be set before including internal.h
+	  because internal.h includes ruby.h, ruby.h includes win32.h, and
+	  win32.h includes system's math.h.
+	  this change is to get rid of a compiler warning (redefinition of
+	  a macro) introduced at r55641.
+
 Wed Jul 13 15:19:03 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* enc/iso_8859_1.c, enc/iso_8859_4.c: Avoid setting modification flag if
diff --git a/math.c b/math.c
index 87d487d8a6..a781167d5e 100644
--- a/math.c
+++ b/math.c
@@ -9,10 +9,10 @@
 
 **********************************************************************/
 
-#include "internal.h"
 #ifdef _MSC_VER
 # define _USE_MATH_DEFINES 1
 #endif
+#include "internal.h"
 #include <float.h>
 #include <math.h>
 #include <errno.h>