diff --git a/Library/Homebrew/os/mac/xcode.rb b/Library/Homebrew/os/mac/xcode.rb
index 03467b98a5..de710728c9 100644
--- a/Library/Homebrew/os/mac/xcode.rb
+++ b/Library/Homebrew/os/mac/xcode.rb
@@ -169,11 +169,16 @@ module OS
 
       # True if:
       #  - Xcode < 4.3 is installed. The tools are found under /usr.
-      #  - The "Command Line Tools" package has been installed
-      #    For OS X < 10.9, the tools are found under /usr. For 10.9,
-      #    they are found under /Library/Developer/CommandLineTools.
+      #  - The "Command Line Tools" package has been installed.
+      #    For OS X < 10.9, the tools are found under /usr. 10.9 always
+      #    includes tools there, which run the real tools inside Xcode on
+      #    Xcode-only installs, so it's necessary to look elsewhere.
       def installed?
-        mavericks_dev_tools? || usr_dev_tools?
+        if MacOS.version < :mavericks
+          usr_dev_tools?
+        else
+          mavericks_dev_tools?
+        end
       end
 
       def mavericks_dev_tools?