diff --git a/libraries/AP_Common/AP_Common.h b/libraries/AP_Common/AP_Common.h
index 2b7c7436d4..df9c697dc0 100644
--- a/libraries/AP_Common/AP_Common.h
+++ b/libraries/AP_Common/AP_Common.h
@@ -191,6 +191,7 @@ protected:
 /// XXX this should probably be replaced with radians()/degrees(), but their
 /// inclusion in wiring.h makes doing that here difficult.
 #define ToDeg(x) (x*57.2957795131)	// *180/pi
+#define ToRad(x) (x*0.01745329252)	// *pi/180
 
 //@}