diff --git a/lib/openid/dh.rb b/lib/openid/dh.rb
index cbe53114..0c15b867 100644
--- a/lib/openid/dh.rb
+++ b/lib/openid/dh.rb
@@ -57,7 +57,7 @@ def DiffieHellman.strxor(s, t)
       end
 
       if String.method_defined? :bytes
-        s.bytes.zip(t.bytes).map{|sb,tb| sb^tb}.pack('C*')
+        s.bytes.to_a.zip(t.bytes.to_a).map{|sb,tb| sb^tb}.pack('C*')
       else
         indices = 0...(s.length)
         chrs = indices.collect {|i| (s[i]^t[i]).chr}