diff --git a/progs/demos/engine.c b/progs/demos/engine.c
index 143b02a8894..68c4d500dfa 100644
--- a/progs/demos/engine.c
+++ b/progs/demos/engine.c
@@ -16,6 +16,10 @@
 #include "trackball.h"
 
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
 #define DEG_TO_RAD(DEG)  ((DEG) * M_PI / 180.0)
 
 #define TEXTURE_FILE "../images/reflect.rgb"