diff --git a/contrib/pgbench/pgbench.c b/contrib/pgbench/pgbench.c
index ad55c3cc03..c0e5e24fff 100644
--- a/contrib/pgbench/pgbench.c
+++ b/contrib/pgbench/pgbench.c
@@ -53,6 +53,10 @@
 #define INT64_MAX	INT64CONST(0x7FFFFFFFFFFFFFFF)
 #endif
 
+#ifndef M_PI
+#define M_PI 3.14159265358979323846
+#endif
+
 /*
  * Multi-platform pthread implementations
  */