diff --git a/lib/tasks/locales.rake b/lib/tasks/locales.rake
index 7f7afa1a8..541f5b2f0 100644
--- a/lib/tasks/locales.rake
+++ b/lib/tasks/locales.rake
@@ -59,6 +59,9 @@ namespace :locales do
   desc <<-END_DESC
 Removes a translation string from all locale file (only works for top-level childless non-multiline keys, probably doesn\'t work on windows).
 
+This task does not work on Ruby 1.8.6.
+You need to use Ruby 1.8.7 or later.
+
 Options:
   key=key_1,key_2    Comma-separated list of keys to delete
   skip=en,de         Comma-separated list of locale files to ignore (filename without extension)