1 files changed, 3 insertions, 1 deletions
diff --git a/lib/resolv.rb b/lib/resolv.rb
index 3f3ed41a47..08bfde583b 100644
--- a/lib/resolv.rb
+++ b/lib/resolv.rb
@@ -1170,7 +1170,9 @@ class Resolv
       class Str # :nodoc:
         def initialize(string)
           @string = string
-          @downcase = string.downcase
+          # case insensivity of DNS labels doesn't apply non-ASCII characters. [RFC 4343]
+          # This assumes @string is given in ASCII compatible encoding.
+          @downcase = string.dup.force_encoding('ASCII-8BIT').downcase
         end
         attr_reader :string, :downcase