diff --git a/Library/Homebrew/blacklist.rb b/Library/Homebrew/blacklist.rb
index 8cd3b1a2db..a6b3379f1e 100644
--- a/Library/Homebrew/blacklist.rb
+++ b/Library/Homebrew/blacklist.rb
@@ -39,5 +39,13 @@ def blacklisted? name
     Xcode can be installed via the App Store (on Lion or newer), or from:
       http://connect.apple.com/
     EOS
+  when 'gtest', 'googletest', 'google-test' then <<-EOS.undent
+    Installing gtest system-wide is not recommended; it should be vendored
+    in your projects that use it.
+    EOS
+  when 'gmock', 'googlemock', 'google-mock' then <<-EOS.undent
+    Installing gmock system-wide is not recommended; it should be vendored
+    in your projects that use it.
+    EOS
   end
 end