diff --git a/Examples/perl5/shadow/example.cxx b/Examples/perl5/shadow/example.cxx
index d7f5046fe..bf088228f 100644
--- a/Examples/perl5/shadow/example.cxx
+++ b/Examples/perl5/shadow/example.cxx
@@ -2,6 +2,9 @@
 
 #include "example.h"
 #include <math.h>
+#ifndef M_PI
+#  define M_PI 3.14159265358979323846
+#endif
 
 /* Move the shape to a new location */
 void Shape::move(double dx, double dy) {