diff --git a/tools/rbcrun/cmd/rbcrun.go b/tools/rbcrun/cmd/rbcrun.go
index 7848562..4db6a0b 100644
--- a/tools/rbcrun/cmd/rbcrun.go
+++ b/tools/rbcrun/cmd/rbcrun.go
@@ -93,6 +93,6 @@
 }
 
 func quit(format string, s ...interface{}) {
-	fmt.Fprintln(os.Stderr, format, s)
+	fmt.Fprintf(os.Stderr, format, s...)
 	os.Exit(2)
 }