diff --git a/src/calibre/ebooks/mobi/utils.py b/src/calibre/ebooks/mobi/utils.py
index ae8e583a1b..dfdb73fdff 100644
--- a/src/calibre/ebooks/mobi/utils.py
+++ b/src/calibre/ebooks/mobi/utils.py
@@ -302,7 +302,7 @@ def encode_tbs(val, extra, flag_size=4):
         ans += encint(extra[0b0001])
     return ans
 
-def utf8_text(text):
+def utf8_text(text, empty=False):
     '''
     Convert a possibly null string to utf-8 bytes, guaranteeing to return a non
     empty, normalized bytestring.
@@ -313,7 +313,10 @@ def utf8_text(text):
             text = text.decode('utf-8', 'replace')
         text = normalize(text).encode('utf-8')
     else:
-        text = _('Unknown').encode('utf-8')
+        if not empty:
+            text = _('Unknown').encode('utf-8')
+        else:
+            text = u''.encode('utf-8') # yeah, stupid
     return text
 
 def align_block(raw, multiple=4, pad=b'\0'):
diff --git a/src/calibre/ebooks/mobi/writer2/serializer.py b/src/calibre/ebooks/mobi/writer2/serializer.py
index 5251bf934f..87b42cd601 100644
--- a/src/calibre/ebooks/mobi/writer2/serializer.py
+++ b/src/calibre/ebooks/mobi/writer2/serializer.py
@@ -355,7 +355,7 @@ class Serializer(object):
         text = text.replace(u'\u00AD', '') # Soft-hyphen
         if quot:
             text = text.replace('"', '"')
-        self.buf.write(utf8_text(text))
+        self.buf.write(utf8_text(text, empty=True))
 
     def fixup_links(self):
         '''