diff --git a/complex.c b/complex.c
index 50d53afcde..beaf6713a1 100644
--- a/complex.c
+++ b/complex.c
@@ -5,12 +5,12 @@
   which is written in ruby.
 */
 
-#include "internal.h"
 #if defined _MSC_VER
 /* Microsoft Visual C does not define M_PI and others by default */
 # define _USE_MATH_DEFINES 1
 #endif
 #include <math.h>
+#include "internal.h"
 
 #define NDEBUG
 #include <assert.h>
diff --git a/include/ruby/missing.h b/include/ruby/missing.h
index 161d95430a..f9e9daed3a 100644
--- a/include/ruby/missing.h
+++ b/include/ruby/missing.h
@@ -37,6 +37,13 @@ extern "C" {
 #endif
 #endif
 
+#ifndef M_PI
+# define M_PI 3.14159265358979323846
+#endif
+#ifndef M_PI_2
+# define M_PI_2 (M_PI/2)
+#endif
+
 #ifndef RUBY_SYMBOL_EXPORT_BEGIN
 # define RUBY_SYMBOL_EXPORT_BEGIN /* begin */
 # define RUBY_SYMBOL_EXPORT_END   /* end */
diff --git a/math.c b/math.c
index 22bd731745..134d937358 100644
--- a/math.c
+++ b/math.c
@@ -106,9 +106,6 @@ num2dbl_with_to_f(VALUE num)
 static VALUE
 math_atan2(VALUE obj, VALUE y, VALUE x)
 {
-#ifndef M_PI
-# define M_PI 3.14159265358979323846
-#endif
     double dx, dy;
     dx = Get_Double(x);
     dy = Get_Double(y);