diff --git a/progs/demos/engine.c b/progs/demos/engine.c
index 393cd95988f..6040a2f1030 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"
diff --git a/progs/xdemos/corender.c b/progs/xdemos/corender.c
index 02e4ac02162..f2b8145e52b 100644
--- a/progs/xdemos/corender.c
+++ b/progs/xdemos/corender.c
@@ -26,6 +26,10 @@
 #include "ipc.h"
 
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
 static int MyID = 0;  /* 0 or 1 */
 static int WindowID = 0;
 static GLXContext Context = 0;