diff --git a/lib/csv.rb b/lib/csv.rb
index fe15315..43d77d8 100644
--- a/lib/csv.rb
+++ b/lib/csv.rb
@@ -2017,10 +2017,13 @@ class CSV
     @force_quotes   = options.delete(:force_quotes)
     do_quote        = lambda do |field|
       field         = String(field)
-      encoded_quote = @quote_char.encode(field.encoding)
-      encoded_quote                                +
-      field.gsub(encoded_quote, encoded_quote * 2) +
-      encoded_quote
+      field_encoding = field.encoding
+      if field_encoding.ascii_compatible?
+        encoded_quote = @quote_char
+      else
+        encoded_quote = @quote_char.encode(field_encoding)
+      end
+      "#{encoded_quote}#{field.gsub(encoded_quote, '\&\&')}#{encoded_quote}"
     end
     quotable_chars = encode_str("\r\n", @col_sep, @quote_char)
     @quote         = if @force_quotes