diff --git a/src/calibre/ebooks/metadata/mobi.py b/src/calibre/ebooks/metadata/mobi.py
index ffdef77d11..15fdceff15 100644
--- a/src/calibre/ebooks/metadata/mobi.py
+++ b/src/calibre/ebooks/metadata/mobi.py
@@ -259,6 +259,7 @@ class MetadataUpdater(object):
         trail = len(new_record0.getvalue()) % 4
         pad = '\0' * (4 - trail) # Always pad w/ at least 1 byte
         new_record0.write(pad)
+        new_record0.write('\0'*(1024*8))
 
         # Rebuild the stream, update the pdbrecords pointers
         self.patchSection(0,new_record0.getvalue())
diff --git a/src/calibre/ebooks/mobi/debug.py b/src/calibre/ebooks/mobi/debug.py
index 36aba39d65..86ed3e9ef9 100644
--- a/src/calibre/ebooks/mobi/debug.py
+++ b/src/calibre/ebooks/mobi/debug.py
@@ -274,7 +274,7 @@ class MOBIHeader(object):
             self.exth = EXTHHeader(self.raw[self.exth_offset:])
 
             self.end_of_exth = self.exth_offset + self.exth.length
-            self.bytes_after_exth = len(self.raw) - self.end_of_exth
+            self.bytes_after_exth = self.fullname_offset - self.end_of_exth
 
     def __str__(self):
         ans = ['*'*20 + ' MOBI Header '+ '*'*20]
@@ -321,6 +321,9 @@ class MOBIHeader(object):
             ans += '\n\n' + str(self.exth)
             ans += '\n\nBytes after EXTH: %d'%self.bytes_after_exth
 
+        ans += '\nNumber of bytes after full name: %d' % (len(self.raw) - (self.fullname_offset +
+                self.fullname_length))
+
         ans += '\nRecord 0 length: %d'%len(self.raw)
         return ans
 
diff --git a/src/calibre/ebooks/mobi/writer.py b/src/calibre/ebooks/mobi/writer.py
index fc47b26c02..ddcba63eca 100644
--- a/src/calibre/ebooks/mobi/writer.py
+++ b/src/calibre/ebooks/mobi/writer.py
@@ -1511,7 +1511,7 @@ class MobiWriter(object):
         record0.write(exth)
         record0.write(title)
         record0 = record0.getvalue()
-        self._records[0] = record0 + ('\0' * (2452 - len(record0)))
+        self._records[0] = record0 + ('\0' * (1024*8))
 
     def _build_exth(self):
         oeb = self._oeb