diff --git a/ext/date/prereq.mk b/ext/date/prereq.mk
index fa371e0..eb71e55 100644
--- a/ext/date/prereq.mk
+++ b/ext/date/prereq.mk
@@ -9,4 +9,4 @@ zonetab.h: zonetab.list
 
 .PHONY: update-zonetab
 update-zonetab:
-	$(RUBY) -C $(srcdir) update-abbr.rb
+	$(RUBY) -C $(srcdir) update-abbr