diff --git a/hypopg.c b/hypopg.c
index 8fe09da..8d3e2ee 100644
--- a/hypopg.c
+++ b/hypopg.c
@@ -14,6 +14,7 @@
  */
 
 #include <unistd.h>
+#include <math.h>
 
 #include "postgres.h"
 #include "fmgr.h"