--- a/fdlibm.h	2022-12-13 14:27:29.092805897 -0500
+++ b/fdlibm.h	2022-12-13 14:27:37.444836016 -0500
@@ -9,18 +9,21 @@
  * ====================================================
  */
 
 /*
  * from: @(#)fdlibm.h 5.1 93/09/24
  * $FreeBSD$
  */
 
-#ifndef _MATH_H_
-#define	_MATH_H_
+#ifndef mozilla_imported_fdlibm_h
+#define	mozilla_imported_fdlibm_h

+#ifndef M_PI_2
 #define	M_PI_2		1.57079632679489661923	/* pi/2 */
+#endif
+
 double	acos(double);
 double	asin(double);
 double	atan(double);
 double	atan2(double, double);
 double	cos(double);
 double	sin(double);
@@ -69,9 +72,9 @@
 float	ceilf(float);
 float	fabsf(float);
 float	floorf(float);
 float	nearbyintf(float);
 float	rintf(float);
 float	scalbnf(float, int);
 float	truncf(float);
 
-#endif /* !_MATH_H_ */
+#endif /* !mozilla_imported_fdlibm_h */