diff --git a/Makefile b/Makefile
index 057a5f5..a83d416 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 frfac:
-	sed "1d;2i #!`./latest_perl`" frfac.in > frfac
+	sed '1s@^.*$$@\#\!'$$(latest_perl)@ frfac.in > frfac
 
 check:
 	`./latest_perl` -wc frfac.in