diff --git a/src/calibre/ebooks/mobi/utils.py b/src/calibre/ebooks/mobi/utils.py
index dfdb73fdff..ae8e583a1b 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, empty=False):
+def utf8_text(text):
     '''
     Convert a possibly null string to utf-8 bytes, guaranteeing to return a non
     empty, normalized bytestring.
@@ -313,10 +313,7 @@ def utf8_text(text, empty=False):
             text = text.decode('utf-8', 'replace')
         text = normalize(text).encode('utf-8')
     else:
-        if not empty:
-            text = _('Unknown').encode('utf-8')
-        else:
-            text = u''.encode('utf-8') # yeah, stupid
+        text = _('Unknown').encode('utf-8')
     return text
 
 def align_block(raw, multiple=4, pad=b'\0'):