diff --git a/src/calibre/ebooks/pdb/formatreader.py b/src/calibre/ebooks/pdb/formatreader.py
index b3f4b059f4..1d14c630de 100644
--- a/src/calibre/ebooks/pdb/formatreader.py
+++ b/src/calibre/ebooks/pdb/formatreader.py
@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 '''
 Interface defining the necessary public functions for a pdb format reader.
diff --git a/src/calibre/ebooks/pdf/__init__.py b/src/calibre/ebooks/pdf/__init__.py
index 26990d63bc..c23e175ece 100644
--- a/src/calibre/ebooks/pdf/__init__.py
+++ b/src/calibre/ebooks/pdf/__init__.py
@@ -1,4 +1,6 @@
 #!/usr/bin/env  python2
+from __future__ import absolute_import, division, print_function, unicode_literals
+
 __license__   = 'GPL v3'
 __copyright__ = '2008, Kovid Goyal kovid@kovidgoyal.net'
 __docformat__ = 'restructuredtext en'
@@ -6,4 +8,3 @@ __docformat__ = 'restructuredtext en'
 '''
 Used for pdf output for comic2pdf
 '''
-
diff --git a/src/calibre/ebooks/pdf/reflow.py b/src/calibre/ebooks/pdf/reflow.py
index 54c44ebe3c..7c776f15a6 100644
--- a/src/calibre/ebooks/pdf/reflow.py
+++ b/src/calibre/ebooks/pdf/reflow.py
@@ -1,6 +1,6 @@
 #!/usr/bin/env python2
 # vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
-from __future__ import with_statement
+from __future__ import absolute_import, division, print_function, unicode_literals
 
 __license__   = 'GPL v3'
 __copyright__ = '2009, Kovid Goyal <kovid@kovidgoyal.net>'
diff --git a/src/calibre/ebooks/pdf/render/common.py b/src/calibre/ebooks/pdf/render/common.py
index 35d16d9280..1b5f66c239 100644
--- a/src/calibre/ebooks/pdf/render/common.py
+++ b/src/calibre/ebooks/pdf/render/common.py
@@ -69,7 +69,7 @@ def serialize(o, stream):
         # Must check bool before int as bools are subclasses of int
         stream.write_raw(b'true' if o else b'false')
     elif isinstance(o, numbers.Integral):
-        stream.write_raw(str(o).encode('ascii') if ispy3 else bytes(o))
+        stream.write_raw(unicode_type(o).encode('ascii') if ispy3 else bytes(o))
     elif hasattr(o, 'pdf_serialize'):
         o.pdf_serialize(stream)
     elif o is None:
diff --git a/src/calibre/ebooks/pdf/render/from_html.py b/src/calibre/ebooks/pdf/render/from_html.py
index 16e9442f1d..556c44219d 100644
--- a/src/calibre/ebooks/pdf/render/from_html.py
+++ b/src/calibre/ebooks/pdf/render/from_html.py
@@ -419,7 +419,7 @@ class PDFWriter(QObject):
                 self.paged_js += P('viewer/hyphenate/Hyphenator.js', data=True).decode('utf-8')
                 hjs, self.hyphenate_lang = load_hyphenator_dicts({}, self.book_language)
                 self.paged_js += hjs
-            self.hf_uuid = str(uuid.uuid4()).replace('-', '')
+            self.hf_uuid = unicode_type(uuid.uuid4()).replace('-', '')
 
         self.view.page().mainFrame().addToJavaScriptWindowObject("py_bridge", self)
         self.view.page().longjs_counter = 0