diff --git a/heat/engine/clients/os/nova.py b/heat/engine/clients/os/nova.py
index 7a8c1a24ab..4a8c58eb29 100644
--- a/heat/engine/clients/os/nova.py
+++ b/heat/engine/clients/os/nova.py
@@ -301,7 +301,15 @@ class NovaClientPlugin(client_plugin.ClientPlugin):
                 subtype = os.path.splitext(filename)[0]
             if content is None:
                 content = ''
-            msg = text.MIMEText(content, _subtype=subtype)
+
+            try:
+                content.encode('us-ascii')
+                charset = 'us-ascii'
+            except UnicodeEncodeError:
+                charset = 'utf-8'
+            msg = (text.MIMEText(content, _subtype=subtype, _charset=charset)
+                   if subtype else text.MIMEText(content, _charset=charset))
+
             msg.add_header('Content-Disposition', 'attachment',
                            filename=filename)
             return msg
diff --git a/heat/engine/resources/openstack/heat/multi_part.py b/heat/engine/resources/openstack/heat/multi_part.py
index 09c8bf0f16..0bd8c9a16e 100644
--- a/heat/engine/resources/openstack/heat/multi_part.py
+++ b/heat/engine/resources/openstack/heat/multi_part.py
@@ -154,8 +154,15 @@ class MultipartMime(software_config.SoftwareConfig):
 
     @staticmethod
     def _create_message(part, subtype, filename):
-        msg = (text.MIMEText(part, _subtype=subtype)
-               if subtype else text.MIMEText(part))
+        charset = 'us-ascii'
+        try:
+            part.encode(charset)
+        except UnicodeEncodeError:
+            charset = 'utf-8'
+        msg = (text.MIMEText(part, _subtype=subtype,
+                             _charset=charset)
+               if subtype else text.MIMEText(part, _charset=charset))
+
         if filename:
             msg.add_header('Content-Disposition', 'attachment',
                            filename=filename)