diff --git a/libexec/atrun/gloadavg.c b/libexec/atrun/gloadavg.c
index 6cffe5a4cfe..f75c3331cf2 100644
--- a/libexec/atrun/gloadavg.c
+++ b/libexec/atrun/gloadavg.c
@@ -44,7 +44,7 @@ static const char rcsid[] =
 
 /* Global functions */
 
-void perr(const char *a);
+void perr(const char *fmt, ...);
 
 double
 gloadavg(void)