diff --git a/book/07-git-tools/git-credential-read-only b/book/07-git-tools/git-credential-read-only
index b98833c4e..9e984dca9 100755
--- a/book/07-git-tools/git-credential-read-only
+++ b/book/07-git-tools/git-credential-read-only
@@ -11,7 +11,7 @@ OptionParser.new do |opts|
 end.parse!
 
 exit(0) unless ARGV[0].downcase == 'get' # <2>
-exit(0) unless File.exists? path
+exit(0) unless File.exist? path
 
 known = {} # <3>
 while line = STDIN.gets