diff --git a/lib/docopt.rb b/lib/docopt.rb
index dee2744..ab3a75f 100644
--- a/lib/docopt.rb
+++ b/lib/docopt.rb
@@ -579,7 +579,7 @@ def parse_defaults(doc)
     end
 
     def printable_usage(doc)
-      usage_split = doc.split(/([Uu][Ss][Aa][Gg][Ee]:)/)
+      usage_split = doc.split(/(Usage:)/i)
       if usage_split.count < 3
         raise DocoptLanguageError, '"usage:" (case-insensitive) not found.'
       end