diff --git a/lib/em-websocket/masking04.rb b/lib/em-websocket/masking04.rb
index d4974b0..ad050e9 100644
--- a/lib/em-websocket/masking04.rb
+++ b/lib/em-websocket/masking04.rb
@@ -15,10 +15,6 @@ def unset_mask
         @masking_key = nil
       end
 
-      def slice_mask
-        slice!(0, 4)
-      end
-
       def getbyte(index)
         if defined?(@masking_key) && @masking_key
           masked_char = super