diff --git a/rubyrrdtool.c b/rubyrrdtool.c
index 6afef68..fb14dea 100644
--- a/rubyrrdtool.c
+++ b/rubyrrdtool.c
@@ -49,7 +49,7 @@ typedef int (*RRDtoolFUNC)(int argc, char ** argv);
  * define macros for easy error checking
  */
 
-#define RRD_RAISE  rb_raise(rb_eRRDtoolError, rrd_get_error());
+#define RRD_RAISE  rb_raise(rb_eRRDtoolError, "%s", rrd_get_error());
 
 #define RRD_CHECK_ERROR  if (rrd_test_error()) RRD_RAISE