diff a/src/rrd_format.h b/src/rrd_format.h
--- a/src/rrd_format.h
+++ b/src/rrd_format.h
@@ -36,5 +36,5 @@
 #define RRD_VERSION   "0004"
 #define RRD_VERSION3  "0003"
-#define FLOAT_COOKIE  8.642135E130
+#define FLOAT_COOKIE  ((double)8.642135E130)
 
 typedef union unival {