diff --git a/pic2plot/gram.yy b/pic2plot/gram.yy

index d11320b..1bcce46 100644

--- a/pic2plot/gram.yy

+++ b/pic2plot/gram.yy

@@ -1833,7 +1833,7 @@ do_sprintf(const char *form, const double *v, int nv)

 	    {

 	      one_format += *form++;

 	      one_format += '\0';

-	      sprintf(sprintf_buf, one_format.contents());

+	      sprintf(sprintf_buf, "%s", one_format.contents());

 	    }

 	  else 

 	    {