diff --git a/lib/xcode/install.rb b/lib/xcode/install.rb
index 09ba9a50..e6ee5163 100644
--- a/lib/xcode/install.rb
+++ b/lib/xcode/install.rb
@@ -62,7 +62,7 @@ def installed?(version)
     end
 
     def installed_versions
-      installed.map { |x| InstalledXcode.new(x) }.sort do |a, b|
+      @installed ||= installed.map { |x| InstalledXcode.new(x) }.sort do |a, b|
         Gem::Version.new(a.version) <=> Gem::Version.new(b.version)
       end
     end