diff --git a/docs/Formula-Cookbook.md b/docs/Formula-Cookbook.md
index 81e30f56a0..43bf92ad2c 100644
--- a/docs/Formula-Cookbook.md
+++ b/docs/Formula-Cookbook.md
@@ -441,7 +441,7 @@ inreplace "path", before, after
 
 ```ruby
 inreplace "path" do |s|
-  s.gsub! /foo/, "bar"
+  s.gsub!(/foo/, "bar")
   s.gsub! "123", "456"
 end
 ```