diff --git a/lib/csv.rb b/lib/csv.rb
index e5ecf5c..7d77079 100644
--- a/lib/csv.rb
+++ b/lib/csv.rb
@@ -1502,6 +1502,7 @@ class CSV
                   when /\A[^:]+/; Encoding.find($&)
                   end ) ||
                 Encoding.default_internal || Encoding.default_external
+    @force_encoding = !!options.delete(:force_encoding)
     #
     # prepare for building safe regular expressions in the target encoding,
     # if we can transcode the needed characters
@@ -1605,6 +1606,11 @@ class CSV
   attr_reader :encoding
 
   #
+  # The flag to encode inserted strings forcibly.
+  #
+  attr_reader :force_encoding
+
+  #
   # The line number of the last row read from this file.  Fields with nested
   # line-end characters will not affect this count.
   #
@@ -1656,10 +1662,13 @@ class CSV
 
     output = row.map(&@quote).join(@col_sep) + @row_sep  # quote and separate
     if @io.is_a?(StringIO)             and
-       output.encoding != raw_encoding and
-       (compatible_encoding = Encoding.compatible?(@io.string, output))
-      @io.set_encoding(compatible_encoding)
-      @io.seek(0, IO::SEEK_END)
+       output.encoding != raw_encoding
+      if force_encoding
+        output = output.force_encoding(raw_encoding)
+      elsif compatible_encoding = Encoding.compatible?(@io.string, output)
+        @io.set_encoding(compatible_encoding)
+        @io.seek(0, IO::SEEK_END)
+      end
     end
     @io << output