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