diff --git a/lib/mapi/mime.rb b/lib/mapi/mime.rb
index 3271de8..96c0b07 100644
--- a/lib/mapi/mime.rb
+++ b/lib/mapi/mime.rb
@@ -97,7 +97,12 @@ def to_s opts={}
   		opts = {:boundary_counter => 0}.merge opts
   		if multipart?
   			boundary = Mime.make_boundary opts[:boundary_counter] += 1, self
-  			@body = [preamble, parts.map { |part| "\r\n" + part.to_s(opts) + "\r\n" }, "--\r\n" + epilogue].
+			#ensure that all parts are utf-8
+			fallback = Hash.new {'?'}
+			fallback["\u2014"] = "-"
+  			@body = [preamble, parts.map { |part| 
+				"\r\n" + part.to_s(opts).encode('UTF-8', fallback: fallback) + "\r\n"
+			}, "--\r\n" + epilogue].
   				flatten.join("\r\n--" + boundary)
   			content_type, attrs = Mime.split_header @headers['Content-Type'][0]
   			attrs['boundary'] = boundary
diff --git a/lib/mapi/version.rb b/lib/mapi/version.rb
index e94f97c..0653d07 100644
--- a/lib/mapi/version.rb
+++ b/lib/mapi/version.rb
@@ -1,3 +1,3 @@
 module Mapi
-	VERSION = '1.5.2'
+	VERSION = '1.5.3'
 end